CALCTHRUM

Solve five number fields. Their answers become the final puzzle in the centre. Practise addition, multiplication or both, with spoken equations and five levels.

Five answers lead to one final equation. In each outer pentagon of CALCTHRUM, find the number made by adding or multiplying two other numbers in the same field. Tap the answer. Your five answers move to the centre, where they form a new puzzle with one correct solution.

Choose Plus, Times or Mixed and one of five levels. Each field contains five different numbers. Mixed uses addition and multiplication in the outer fields and addition in the centre. Times also uses multiplication for the final puzzle.

Press Start when you are ready. The clock runs during play and pauses while help, settings or statistics are open. During a round the number board fills the screen; an arrow at the top left ends the round. Solve the centre to see your stopped time and the final equation, followed by the celebration sound and confetti. You can then inspect all six equations.

Turn sound on to hear the matching equation after each correct answer. Switch between German and English in settings, or turn sound off. Both languages and all voice recordings are included in the app.

Statistics show completed puzzles, times and incorrect attempts. They stay on your device. Puzzles are generated on the device too, so you can play offline without an account.

Practise mental arithmetic without advertising, in-app purchases or tracking. Play on iPhone or iPad in portrait or landscape. Landscape places the instructions and timer to the left of the number board.

CALCTHRUM is a learning app from Dachverband Legasthenie Deutschland e.V. (DVLD), a non-profit dyslexia association.

Each wrong attempt adds a 10-second penalty to your round time. Final time, best time and average include these penalties. Crossing out and hints add no time.