Rechenbuch

Rechenbuch is a calculator that takes the fold of iPhone Duo seriously.

Folded, it works like a good desk calculator. The result appears only after “=”, and every calculation lands on a paper tape you can check, share as text or print as a PDF. A protective cover slides over the outer display and locks the keys in your pocket, while its window keeps showing the result.

Unfolded, it becomes a book. Tabs with scientific functions sit on the left, the keypad on the right. Stand it up and the top half draws graphs. Lay it flat on the table and the left page turns into a notebook where variables and units calculate along.

What’s inside:
• Paper tape with step-by-step working, export as text or PDF
• Scientific functions, degrees or radians always visible
• Equation solver, also for other variables. Linear and quadratic equations come out exact, with roots or fractions
• Graphs with sliders, zeros, maxima, minima and intersections
• School formula sheet, each formula with a short explanation. Leave one field empty and Rechenbuch works it out
• Converter for amounts and units, from teaspoons to kilowatt-hours
• Notebook with variables and units: width = 4.2 m, depth = 3.1 m, area = width × depth
• Statistics, physical constants, bit operations from 8 to 64 bits
• Sales tax in one tap, rounding you choose and can see
• Exam mode that locks graphs, the equation solver, variables and the notebook
• Widget with your last result
• Left-handed mode, large text, VoiceOver, English and German

Every other iPhone and iPad gets the same features, iPad with book view and desk mode.

No ads, no account, no data collection. Your calculations stay on your device.