This page about the Android app "Plus Minus Times Divide" (PMTD for short) is not meant to be nice or good looking (and is in this regard probably quite successful) but rather to provide some information.
Should it be in this last regard not so successful, the helpful reader should not hesitate to contact me through the app itself, using the menu entry "About...".
In short, PMTD is an Android app to train children's skills in the four calculation operations.
More extensively explained, it is an Android program to train children's mathematical skills in the four calculation methods: addition, subtraction, multiplication and division. The preferences allow to adapt the app's difficulty to any pupil's level, from basic primary (elementary) school to secondary and beyond.
The program gives hints when the given answer is wrong (send me your tips if you have some more). The preferences dialog (from the Menu button) allows adaptation to most levels of difficulty required by children in different ages:
There is a timer but it is shut-off by default, as to not stress sensible children. Finally, the language of the app can be set differently (English, French, German) from the system default.
I'm currently working on a challenge mode which will allow to create pre-defined sets of exercises with a score at the end, a ranking and the ability to check progress over time. The challenge mode can already be used but without ranking and progress yet.
And last but not least, the program and the code are free (Open Source) under the GNU GPL Version 3 or later License (GPLv3+).
The easiest way is surely to install the app from the Google Play or from F-Droid (an Open Source-only alternative) and to take the source code (starting with version 2012.12.18.20) from Google Code.
The last app version can additionally be found on this server, which can allow you to install it manually, should the installation from unknown sources have been allowed.
Moreover can older versions of the source code also be found here.
A list of all changes is available as well.