diff --git a/roles/calibre/defaults/main.yml b/roles/calibre/defaults/main.yml
index 8cafdb995..f135ee6f2 100644
--- a/roles/calibre/defaults/main.yml
+++ b/roles/calibre/defaults/main.yml
@@ -12,7 +12,7 @@ calibre_sample_book: "Metamorphosis-jackson.epub"
 
 calibre_src_url: "https://raw.githubusercontent.com/kovidgoyal/calibre/master/setup/linux-installer.py"
 
-# USE TO TEST debs.yml (RASPBIAN APPROACH!) ON DEBIAN 9.X
-calibre_debs_on_debian: True
-# enable calibre unstable
-calibre_unstable: False
+# USE TO TEST debs.yml (RASPBIAN APPROACH!) ON DEBIAN 9.X: (now handled by calibre_via_debs in /opt/iiab/iiab/vars/*)
+#calibre_debs_on_debian: True
+# Enable unstable .deb's, not just testing .deb's: (moved to vars/local_vars.yml & vars/default_vars.yml)
+#calibre_unstable_debs: False
diff --git a/roles/calibre/tasks/debs.yml b/roles/calibre/tasks/debs.yml
index ad9917fce..2fdd5cfdc 100644
--- a/roles/calibre/tasks/debs.yml
+++ b/roles/calibre/tasks/debs.yml
@@ -1,24 +1,31 @@
-- name: Start by installing OS's Calibre package
-  package:
-    name: "{{ item }}"
-    state: latest
-  with_items:
-    - calibre
-    - calibre-bin
-  when: internet_available
+# roles/calibre/tasks/main.yml requires calibre_via_debs (to be True) before calling this script.
 
-# April 5 2018 raspbian is now tracking the latest Calibre with a small delay.
-# Should you really want the latest just run the below script standalone, it is
-# strongly suggested that waiting for the lastest deb from Raspbian is the best.
+# MOVED UP TO roles/calibre/tasks/main.yml
+#- name: Start by installing OS's Calibre package
+#  package:
+#    name: "{{ item }}"
+#    state: latest
+#  with_items:
+#    - calibre
+#    - calibre-bin
+#  when: internet_available
 
-- name: Upgrade to testing Calibre - RPi
+# April/May 2018: Raspbian .deb's for the latest Calibre now appear
+# (http://raspbian.raspberrypi.org/raspbian/pool/main/c/calibre/)
+# within about 10 days of Calibre's quasi-monthly releases
+# (https://calibre-ebook.com/whats-new).
+
+# If you want the latest Calibre, run the appropriate below script, standalone.
+# HOWEVER: it's strongly suggested you wait for apt (blessed by your OS!)
+
+- name: Upgrade to Calibre testing .deb's - target Raspbian (rpi)
   command: scripts/calibre-install-latest-rpi.sh
   when: is_rpi and internet_available
 
-- name: Upgrade to testing Calibre - non-RPi
+- name: Upgrade to Calibre testing .deb's - target Ubuntu 16.04 (not rpi and not ubuntu_18)
   command: scripts/calibre-install-latest.sh
   when: not is_rpi and not is_ubuntu_18 and internet_available
 
-- name: Upgrade to unstable Calibre -  all
+- name: Upgrade to Calibre unstable .deb's IF calibre_unstable_debs
   command: scripts/calibre-install-unstable.sh
-  when: calibre_unstable and internet_available
+  when: calibre_unstable_debs and internet_available
diff --git a/roles/calibre/tasks/main.yml b/roles/calibre/tasks/main.yml
index c09aa03ba..74c10c428 100644
--- a/roles/calibre/tasks/main.yml
+++ b/roles/calibre/tasks/main.yml
@@ -1,18 +1,36 @@
-# 1. INSTALL THE LATEST CALIBRE 3.X+ (calibre-server etc) ON ALL OS'S
+# 1. INSTALL THE LATEST CALIBRE 3.X+ (calibre, calibredb, calibre-server etc) ON ALL OS'S
 
-# RUNS IF /usr/bin/calibre-uninstall DOES NOT ALEADY EXIST
-- name: Install Calibre via calibre-installer.py (redhat, ubuntu, debian if NOT calibre_debs_on_debian)
-  include_tasks: py-installer.yml
-  when: is_redhat or is_ubuntu or (is_debian and not calibre_debs_on_debian)
-  #when: not is_rpi
+- name: Check if /usr/bin/calibre exists
+  stat:
+    path: "/usr/bin/calibre"
+  register: calib_executable
 
-- name: Install Calibre via .debs (Raspbian, Debian if calibre_debs_on_debian)
+- name: Install Calibre via OS's package installer (IF /usr/bin/calibre MISSING)
+  package:
+    name: "{{ item }}"
+    state: latest
+  with_items:
+    - calibre
+    - calibre-bin
+  when: internet_available and (not calib_executable.stat.exists)
+
+- name: Install Calibre experimental .debs IF calibre_via_debs (AND /usr/bin/calibre WAS MISSING)
   include_tasks: debs.yml
-  when: is_rpi or (is_debian and calibre_debs_on_debian)
+  when: calibre_via_debs and (not calib_executable.stat.exists)
 
-#- name: Install Calibre via .debs (Ubuntu 18.xx)
-#  include_tasks: debs.yml
-#  when: is_ubuntu_18
+- name: Install Calibre via calibre-installer.py IF calibre_via_python (AND /usr/bin/calibre WAS MISSING)
+  include_tasks: py-installer.yml
+  when: calibre_via_python and (not calib_executable.stat.exists)
+
+# SEE calibre_via_python's value vars/default_vars.yml, vars/ubuntu-18.yml &
+# vars/raspbian-9.yml: try to AVOID Python installer on Raspbian since its
+# .deb's (http://raspbian.raspberrypi.org/raspbian/pool/main/c/calibre/)
+# are updated within about 10 days of Calibre's quasi-monthly releases!
+#
+# BUT IF ABSOLUTELY NEC: (SEE roles/calibre/tasks/debs.yml)
+# - run testing branch for RPi: scripts/calibre-install-latest-rpi.sh
+# - run testing branch for Ubuntu 16.04: scripts/calibre-install-latest.sh
+# - run unstable branch for Debian etc: scripts/calibre-install-unstable.sh
 
 - name: Create calibre-serve.service and calibre.conf
   template:
@@ -27,7 +45,7 @@
     - { src: 'calibre-serve.service.j2', dest: '/etc/systemd/system/calibre-serve.service', mode: '0644'}
     - { src: 'calibre.conf', dest: '/etc/{{ apache_config_dir }}', mode: '0644'}
 
-- name: Forcing systemd to reread configs
+- name: Force systemd to reread configs
   systemd:
     daemon_reload: yes
   when: calibre_config.changed
diff --git a/roles/calibre/tasks/py-installer.yml b/roles/calibre/tasks/py-installer.yml
index 96c3162e5..29f9b3265 100644
--- a/roles/calibre/tasks/py-installer.yml
+++ b/roles/calibre/tasks/py-installer.yml
@@ -1,5 +1,7 @@
+# roles/calibre/tasks/main.yml requires calibre_via_python (to be True) before calling this script.
+
 # Seems to work with just about any Linux (Fedora 18 on OLPC XO Laptops??) and deals with dependencies.
-# But is arch dependent: requires x86_64 or i686 for now.
+# BUT IS ARCH DEPENDENT: requires x86_64 or i686 as of early 2018.
 
 - name: Download latest linux-installer.py from GitHub to calibre-installer.py
   get_url:
@@ -32,21 +34,23 @@
     path: "{{ downloads_dir }}/calibre-installer.py"
   register: calib_inst
 
-- name: Check if calibre-uninstall exists in /usr/bin
-  stat:
-    path: "/usr/bin/calibre-uninstall"
-  register: calib_uninst
+# MOVED UP TO roles/calibre/tasks/main.yml (now checks for /usr/bin/calibre)
+#- name: Check if calibre-uninstall exists in /usr/bin
+#  stat:
+#    path: "/usr/bin/calibre-uninstall"
+#  register: calib_uninst
 
-- name: FAIL (force Ansible to exit) IF /opt/iiab/downloads/calibre-installer.py doesn't exist OR needed Internet connection is missing
+- name: FAIL (force Ansible to exit) IF /opt/iiab/downloads/calibre-installer.py OR Internet ARE MISSING
   # meta: end_play
   fail:
     msg: "{{ downloads_dir }}/calibre-installer.py and an Internet connection are REQUIRED in order to install Calibre!"
-  when: (not calib_inst.stat.exists) or (not internet_available and not calib_uninst.stat.exists)
+  when: (not calib_inst.stat.exists) or (not internet_available)
+  #when: (not calib_inst.stat.exists) or (not internet_available and not calib_uninst.stat.exists)
 
-# INSTALL THE LATEST CALIBRE (calibre-server etc) - RUNS IF /usr/bin/calibre-uninstall DOES NOT ALEADY EXIST
+# INSTALL THE LATEST CALIBRE (calibre, calibredb, calibre-server etc)
 
-- name: Run calibre-installer.py to install Calibre programs into /usr/bin - MANUALLY REMOVE /usr/bin/calibre-uninstall TO FORCE calibre-installer.py TO REINSTALL/UPGRADE HERE!
+- name: Run calibre-installer.py to install Calibre programs into /usr/bin
   shell: "{{ downloads_dir }}/calibre-installer.py >> /dev/null"
-  args:
-    creates: /usr/bin/calibre-uninstall
+  #args:
+  #  creates: /usr/bin/calibre-uninstall
   when: internet_available
diff --git a/scripts/calibre-install-latest-rpi.sh b/scripts/calibre-install-latest-rpi.sh
index 941f29306..a5d520bda 100755
--- a/scripts/calibre-install-latest-rpi.sh
+++ b/scripts/calibre-install-latest-rpi.sh
@@ -1,19 +1,23 @@
 #!/bin/bash
 
-# Thanks to Jerry Vonau (https://github.com/jvonau) who made
-# this critical breakthrough (Calibre 3.x on Raspbian) possible!
-# The latest available is 3.21 available from testing
-# https://packages.debian.org/search?keywords=calibre
-# (SEE http://raspbian.raspberrypi.org/raspbian/pool/main/c/calibre/ 
-#  OR http://archive.raspbian.org/raspbian/pool/main/c/calibre/ ?)
-# Might break future updates, you have been warned.
+# Thanks to Jerry Vonau (https://github.com/jvonau) who made this critical
+# breakthrough possible!
+#
+# Calibre 3.23 is the latest available from testing as of 2018-05-10:
+#
+#   http://raspbian.raspberrypi.org/raspbian/pool/main/c/calibre/
+#   http://archive.raspbian.org/raspbian/pool/main/c/calibre/
+#   https://packages.debian.org/search?keywords=calibre
+#   http://deb.debian.org/debian/pool/main/c/calibre/
+#
+# Might break future updates; you have been warned.
 
 export DEBIAN_FRONTEND=noninteractive
-# Updates calibre calibre-bin to version 3.21 or ... from testing
+# Prepares to update to latest from testing
 echo "deb http://raspbian.raspberrypi.org/raspbian/ testing main" > /etc/apt/sources.list.d/rpi-testing.list
 apt update
 apt -y install calibre calibre-bin
-# Remove last line, safer than: rm /etc/apt/sources.list.d/debian-testing.list
+# Removes last line, safer than: rm /etc/apt/sources.list.d/rpi-testing.list
 sed -i '$ d' /etc/apt/sources.list.d/rpi-testing.list
 # Clears the cache of testing
 apt update
diff --git a/scripts/calibre-install-latest.sh b/scripts/calibre-install-latest.sh
index aebc86ca1..37764db79 100755
--- a/scripts/calibre-install-latest.sh
+++ b/scripts/calibre-install-latest.sh
@@ -1,20 +1,26 @@
 #!/bin/bash
 
-# Thanks to Jerry Vonau (https://github.com/jvonau) who made
-# this critical breakthrough for Calibre 3.x possible!
-# The latest available is 3.20 available from testing
-# https://packages.debian.org/search?keywords=calibre
-# (SEE http://deb.debian.org/debian/pool/main/c/calibre/ ?)
-# might break future updates, you have been warned
+# Thanks to Jerry Vonau (https://github.com/jvonau) who made this critical
+# breakthrough possible!
+#
+# Calibre 3.23 is the latest available from testing as of 2018-05-10:
+#
+#   https://packages.debian.org/search?keywords=calibre
+#   http://deb.debian.org/debian/pool/main/c/calibre/
+#   http://raspbian.raspberrypi.org/raspbian/pool/main/c/calibre/
+#   http://archive.raspbian.org/raspbian/pool/main/c/calibre/
+#
+# Might break future updates; you have been warned.
 
 export DEBIAN_FRONTEND=noninteractive
 # Drags in stock desktop dependencies without too much from testing below
-apt -y install calibre-bin dirmngr
-# Updates calibre calibre-bin to version 3.20 or ... from testing
+apt -y install dirmngr
+# Prepares to update to latest from testing
 apt-key adv --recv-key --keyserver keyserver.ubuntu.com 7638D0442B90D010
 echo "deb http://deb.debian.org/debian testing main" >> /etc/apt/sources.list.d/debian-testing.list
 apt update
-apt -y install libqt5core5a python-lxml calibre
-# Remove last line, safer than: rm /etc/apt/sources.list.d/debian-testing.list
+apt -y install libqt5core5a python-lxml calibre calibre-bin
+# Removes last line, safer than: rm /etc/apt/sources.list.d/debian-testing.list
 sed -i '$ d' /etc/apt/sources.list.d/debian-testing.list
+# Clears the cache of testing
 apt update
diff --git a/scripts/calibre-install-unstable.sh b/scripts/calibre-install-unstable.sh
index c27bfebf5..abb950f7c 100755
--- a/scripts/calibre-install-unstable.sh
+++ b/scripts/calibre-install-unstable.sh
@@ -1,18 +1,24 @@
 #!/bin/bash
 
-# Thanks to Jerry Vonau (https://github.com/jvonau) who made
-# this critical breakthrough possible!
-# might break future updates, you have been warned
-# The latest available is 3.20 available from testing
-# https://packages.debian.org/search?keywords=calibre
-# might break future updates, you have been warned
+# Thanks to Jerry Vonau (https://github.com/jvonau) who made this critical
+# breakthrough possible!
+#
+# Calibre 3.23 is the latest available from testing as of 2018-05-10:
+#
+#   https://packages.debian.org/search?keywords=calibre
+#   http://deb.debian.org/debian/pool/main/c/calibre/
+#   http://raspbian.raspberrypi.org/raspbian/pool/main/c/calibre/
+#   http://archive.raspbian.org/raspbian/pool/main/c/calibre/
+#
+# Might break future updates; you have been warned.
 
 export DEBIAN_FRONTEND=noninteractive
-# Updates to calibre & calibre-bin to "very latest" 3.x from unstable
+# Prepares to update to latest from unstable
+apt-key adv --recv-key --keyserver keyserver.ubuntu.com 7638D0442B90D010
 echo "deb http://deb.debian.org/debian unstable main" >> /etc/apt/sources.list.d/unstable.list
 apt update
 apt -y install calibre calibre-bin
-# Remove last line, safer than: rm /etc/apt/sources.list.d/debian-unstable.list
+# Removes last line, safer than: rm /etc/apt/sources.list.d/unstable.list
 sed -i '$ d' /etc/apt/sources.list.d/unstable.list
 # Clears the cache of testing and unstable
 apt update
diff --git a/vars/centos-7.yml b/vars/centos-7.yml
index 79a654af3..82b7fb824 100644
--- a/vars/centos-7.yml
+++ b/vars/centos-7.yml
@@ -18,3 +18,6 @@ sshd_service: sshd
 php_version: 7.0
 postgresql_version: 9.5
 systemd_location: /usr/lib/systemd/system
+# Upgrade OS's own Calibre to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/debian-8.yml b/vars/debian-8.yml
index 5b6153ce4..7d39b347b 100644
--- a/vars/debian-8.yml
+++ b/vars/debian-8.yml
@@ -18,3 +18,6 @@ sshd_service: ssh
 php_version: 5
 postgresql_version: 9.4
 systemd_location: /lib/systemd/system
+# Upgrade OS's own Calibre to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/debian-9.yml b/vars/debian-9.yml
index a945d779b..6477bf86f 100644
--- a/vars/debian-9.yml
+++ b/vars/debian-9.yml
@@ -19,5 +19,6 @@ sshd_service: ssh
 php_version: 7.0
 postgresql_version: 9.6
 systemd_location: /lib/systemd/system
-
-
+# Upgrade OS's own Calibre to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/default_vars.yml b/vars/default_vars.yml
index 52effee23..c02f7254c 100644
--- a/vars/default_vars.yml
+++ b/vars/default_vars.yml
@@ -242,6 +242,11 @@ idmgr_enables: False
 
 calibre_install: True
 calibre_enabled: True
+# vars/raspbian-9.yml tries the .deb upgrade of Calibre, overriding this default:
+calibre_via_debs: False
+calibre_unstable_debs: False
+# vars/<most-OS's>.yml try the x86_64 python upgrade of Calibre, overriding this default:
+calibre_via_python: False
 # Change calibre_port to 8010 if you're using XO laptops needing above idmgr
 calibre_port: 8080
 # Change calibre to XYZ add your own mnemonic URL like: http://box/XYZ
diff --git a/vars/fedora-18.yml b/vars/fedora-18.yml
index db8395fe9..378463b84 100644
--- a/vars/fedora-18.yml
+++ b/vars/fedora-18.yml
@@ -18,3 +18,6 @@ sshd_service: sshd
 nextcloud_install: False
 nextcloud_enabled: False
 systemd_location: /usr/lib/systemd/system
+# Upgrade OS's own Calibre to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/fedora-22.yml b/vars/fedora-22.yml
index f12a394c2..986a58f1b 100644
--- a/vars/fedora-22.yml
+++ b/vars/fedora-22.yml
@@ -14,3 +14,6 @@ mysql_service: mariadb
 apache_log: /var/log/httpd/access_log
 sshd_service: sshd
 systemd_location: /usr/lib/systemd/system
+# Upgrade OS's own Calibre to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/medium.localvars b/vars/medium.localvars
index f73dfd874..3077cfba5 100644
--- a/vars/medium.localvars
+++ b/vars/medium.localvars
@@ -125,6 +125,11 @@ iiab_usb_lib_show_all: True
 
 calibre_install: True
 calibre_enabled: True
+# Try .deb upgrade of Calibre (like vars/raspbian-9.yml already does)
+# calibre_via_debs: True
+calibre_unstable_debs: False
+# Try python x86_64 upgrade of Calibre (like vars/<most-OS's>.yml already do)
+# calibre_via_python: True
 # Change calibre_port to 8010 if you're using XO laptops needing above idmgr
 calibre_port: 8080
 # Change calibre to XYZ add your own mnemonic URL like: http://box/XYZ
diff --git a/vars/raspbian-8.yml b/vars/raspbian-8.yml
index 1e1e42706..edbdd4606 100644
--- a/vars/raspbian-8.yml
+++ b/vars/raspbian-8.yml
@@ -20,3 +20,8 @@ sshd_service: ssh
 php_version: 5
 postgresql_version: 9.4
 systemd_location: /lib/systemd/system
+# Upgrade Raspbian Jessie's Calibre 2.5.0: (via role/calibre/tasks/debs.yml,
+# with .deb's released about 5-10 days after Calibre's quasi-monthly releases)
+calibre_via_debs: True
+# roles/calibre/tasks/py-installer.yml FAILS on ARM as of 2018-05-10:
+calibre_via_python: False
diff --git a/vars/raspbian-9.yml b/vars/raspbian-9.yml
index bab3f83e0..4cc2d18b1 100644
--- a/vars/raspbian-9.yml
+++ b/vars/raspbian-9.yml
@@ -21,3 +21,8 @@ sshd_service: ssh
 php_version: 7.0
 postgresql_version: 9.6
 systemd_location: /lib/systemd/system
+# Upgrade Raspbian Stretch's Calibre 2.75.1: (via role/calibre/tasks/debs.yml,
+# with .deb's released about 5-10 days after Calibre's quasi-monthly releases)
+calibre_via_debs: True
+# roles/calibre/tasks/py-installer.yml FAILS on ARM as of 2018-05-10:
+calibre_via_python: False
diff --git a/vars/ubuntu-16.yml b/vars/ubuntu-16.yml
index 741e3b012..2d1e28283 100644
--- a/vars/ubuntu-16.yml
+++ b/vars/ubuntu-16.yml
@@ -19,3 +19,6 @@ sshd_service: ssh
 php_version: 7.0
 postgresql_version: 9.5
 systemd_location: /lib/systemd/system
+# Upgrade Ubuntu 16.04's Calibre 2.55.0 to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/ubuntu-17.yml b/vars/ubuntu-17.yml
index 41fd02c1d..ac3b285c7 100644
--- a/vars/ubuntu-17.yml
+++ b/vars/ubuntu-17.yml
@@ -19,3 +19,6 @@ sshd_service: ssh
 php_version: 7.1
 postgresql_version: 9.6
 systemd_location: /lib/systemd/system
+# Upgrade Ubuntu 17.10's Calibre 3.7.0 to very latest:
+calibre_via_debs: False
+calibre_via_python: True
diff --git a/vars/ubuntu-18.yml b/vars/ubuntu-18.yml
index c05df9cf8..9fb269ac9 100644
--- a/vars/ubuntu-18.yml
+++ b/vars/ubuntu-18.yml
@@ -21,3 +21,6 @@ php_version: 7.2
 # "postgresql_version: 10.3" fails (too detailed for /etc/systemd/system/postgresql-iiab.service on Ubuntu 18.04)
 postgresql_version: 10
 systemd_location: /lib/systemd/system
+# Upgrade Ubuntu 18.04's Calibre 3.21.0 to very latest:
+calibre_via_debs: False
+calibre_via_python: True