Developed by Dr Claus Zinn

Computer Scientist and Educational Researcher

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Lehrer Lämpel

Version 1.0
Lehrer Lämpel: Digit Square

An educational app that supports primary school kids to train their skills in basic arithmetic.
  • Practising addition and subtraction, as well as multiplication and division
  • Maximum number of (randomised) exercises (9! = 262880)
  • Intelligent next-step help and error correction
  • Multi-lingual help page (english, german, french)
  • Available for iPad tablets, from iOS8
  • .99 USD, 1.09 Euro
Compatible with the iPad. Requires iOS8 or later. No WiFi, Edge, or 3G network connection required. No ads.


Can you fill-in all the digits so that all calculations are correct? But beware, no digit must occur more than once!

Lehrer Lämpel: Digit Square is an educational app that supports primary school children to practise their skills in basic arithmetic.

Easy input of numbers to the blackboard.

Pupils can ask Lehrer Lämpel for help at any time. Help first signals an erroneously learner step; if there are no errors, a single hint towards the next step of the solution is given.

All teacher steps towards the solution are followed-up with a step explanation as well.

Supports large number (362880) of randomised exercises

Supports English, French and German.

Available on the iPad, for iOS7 or later.


Version 1.0

Released Jan 3rd, 2015
  • Initial Release.

Version 1.1

Released on November 12th, 2015
  • NEWAdded support for iOS9.
  • Improved design


Privacy Policy

Our privacy policy is rather simple. We do not collect any information from you and your child when using our app or browsing our website.

You or your child will never be prompted to provide any sort of information in our app. You are free to use the contact form on the website to give us your feedback, ask questions, elicit new app features, or file a bug report. For this, you can equally contact us at

We will use your contact information only for being able to reply to your requests. It will not be shared with anybody else.

Our app is solely financed by its price tag, there are no in-app purchases, and the app is ads-free.


Contact Us

Please use the following form for questions, feedback, feature requests etc.

Our email:

Postal Address

Dr. Claus Zinn, Diplom-Informatiker (Univ.)
In der Gebhardsoesch 33
78467 Konstanz, Germany