[elinkser]

***


Or, just run a shell script like f2c.sh from the terminal:

#!/mnt/onboard/.adds/koreader/luajit
--f2c.lua
print('*** Converting between the different temperature scales ***')
print('1. Convert Celsius temperature into Fahrenheit')
print('2. Convert Fahrenheit temperatures into Celsius')
print('Select your choice (1-2) : ')
choice = io.read('*n')
if choice==tonumber("1") then
print('Enter temperature (C) : ')
tc = io.read('*n')
-- formula Tf=(9/5)*Tc+32
tf=(9/5) * tc + 32
print('Temperature (F) = ', tf)
elseif choice==tonumber("2") then
print('Enter temperature (F) : ')
tf = io.read('*n')
-- formula Tc=(5/9)*(Tf-32)
tc=(5/9)*(tf-32)
print('Temperature (C) = ', tc)
else
print('Invalid choice')
end


***

Or, from NickelMenu:
(requires NickelDBus .

Add a NickelMenu entry to /mnt/onboard/.adds/nm/config.txt:

menu_item :main :convert :cmd_spawn :quiet:exec /mnt/onboard/.adds/koreader/scripts/convert.sh
    chain_success                      :dbg_toast          :Started convert       
    chain_failure                      :dbg_toast          :Error

And a convert.sh script to /mnt/onboard/.adds/koreader/scripts/:

#!/bin/sh                                        
# convert selection menu
choice=0                              
qndb -m dlgConfirmCreate true                                       
qndb -m dlgConfirmSetTitle "1- Convert Celsius temperature into Fahrenheit; 2- Convert Fahrenheit temperatures into Celsius; Select option (1-2):"
qndb -m dlgConfirmSetLEPlaceholder "1"
qndb -m dlgConfirmShow                           
result=$(qndb -s dlgConfirmTextInput)            
textIn=$(echo $result | sed 's/dlgConfirmTextInput //')
choice=$(echo $textIn | sed 's/[^0-9]//g')
if [ "$choice" == "1" ]; then
	tc=0                              
	qndb -m dlgConfirmCreate true                                       
	qndb -m dlgConfirmSetTitle "Enter temperature (C) : "
	qndb -m dlgConfirmSetLEPlaceholder "0"
	qndb -m dlgConfirmShow                           
	result=$(qndb -s dlgConfirmTextInput)            
	textIn=$(echo $result | sed 's/dlgConfirmTextInput //')
	tc=$(echo $textIn | sed 's/[^0-9\-]//g')
	echo $tc
	tf=$(/mnt/onboard/.adds/koreader/luajit -e "print((9/5) * tonumber($tc) + 32)")
	qndb -m mwcToast 3000 "Temperature (F) = $tf"
elif [ "$choice" == "2" ]; then
	tf=0                              
	qndb -m dlgConfirmCreate true                                       
	qndb -m dlgConfirmSetTitle "Enter temperature (F) : "
	qndb -m dlgConfirmSetLEPlaceholder "0"
	qndb -m dlgConfirmShow                           
	result=$(qndb -s dlgConfirmTextInput)            
	textIn=$(echo $result | sed 's/dlgConfirmTextInput //')
	tf=$(echo $textIn | sed 's/[^0-9\-]//g')
	tc=$(/mnt/onboard/.adds/koreader/luajit -e "print((5/9)*(tonumber($tf)-32))")
	qndb -m mwcToast 3000 "Temperature (C) = $tc"
else
		qndb -m mwcToast 3000 "You selected an invalid option" 
fi
qndb -m mwcToast 1000 "${fberr:-"Bye!"}"

***


Or, make an rmkit Simple App Script:
https://www.mobileread.com/forums/sh...d.php?t=356282

Modify the /mnt/onboard/.adds/rmkit/bin/apps/menu.sh to:

while true; do
  app="
textinput 250 100 200 50 
label 250 200 200 50 you entered: ${temp}
button 150 400 200 50 c2f
button 350 400 200 50 f2c
label 250 600 200 50 you clicked: ${option}
[paragraph 250 800 500 500 Result = ${output}]
"
  echo "APP IS"
  echo "${app}"
  option=`echo "${app}" | /mnt/onboard/.adds/rmkit/bin/apps/simple | grep 'selected:' | sed 's/selected: //'`
  temp=`echo "${app}" | /mnt/onboard/.adds/rmkit/bin/apps/simple | grep 'input:' | sed 's/input: //'`
  if (${option} == "c2f") then
  	output=`/mnt/onboard/.adds/koreader/luajit -e "print((9/5) * tonumber(${temp}) + 32 + ' C')"`
  fi
  if (${option} == "f2c") then
  	output=`/mnt/onboard/.adds/koreader/luajit -e "print((5/9)*(tonumber(${temp}))-32 + ' F')"`
  fi
  sleep 0.1
done

OK, that one didn't actually work...

UPDATE : Now working!
https://www.mobileread.com/forums/sh...57&postcount=8

***



***BEST SOLUTION***

But why all that if you can just:

From:
https://koreader.rocks/user_guide/

Search:
https://github.com/search?q=koplugin&type=repositories
* Edit: on second thought, is unvetted github content becoming a security concern? (re malware found.)

Find:
https://github.com/zwim/calculator.koplugin
zwim/calculator.koplugin

$ wget https://github.com/zwim/calculator.k...ugin-1.2.0.zip

Install:
calculator.koplugin
A calculator plugin for KOReader.

Installation:
Go to https://github.com/zwim/calculator.koplugin/releases and download the desired koreader.plugin-x.x.x.zip and unpack it to koreader/plugins/calculator.koplugin.
Predefined physical constants, are in init.calc. You can autoload them (see settings menu). If you don't need them delete init.calc.

Usage:
You find the calculator in More tools/calculator additionally you can set a gesture (in the device submenu) to call it.


***