Forcing Calculator

This utility lets you set any force number in advance, then hand the calculator out. The handling looks exactly like everyday maths. Your participant taps in a few numbers, presses equals, and the display confirms the outcome you wanted. No phone required. It runs on a single AA battery and resets instantly.

Key benefits

• Force any number with the equals button

• Set the force quickly using the memory function

• Looks and behaves like a normal calculator

• No phone or apps

How it plays

You talk about how people trust maths because it feels objective. A participant enters a short string of numbers drawn from the room or their choices. They press equals. The display matches a prediction you placed in view from the start, or a number they just named. Everything appears fair because they did the tapping and you stayed hands off.

What’s included

• Forcing Calculator (choose Visible M or Taped to hide the memory indicator)

• PDF instructions

Options

• M display: Visible indicator, or taped to hide the “M” when a force is set (suggested by Richard Osterlind)

Specs and practicalities

• Power: 1 × AA battery

• Setup and reset: quick set via memory; resets instantly

• Venues: close up and parlour

• Skill: no sleight of hand; simple audience management; no timing pressure

Handling & pacing

Keep it casual and hands off the buttons. Let the participant input the numbers and press equals. Use the taped option when you want the display to remain visually clean, or keep the “M” visible if you prefer to justify it as a standard memory function.

Requirements

• One AA battery (for orders outside the UK the battery is not included)

History

The core idea in this style of forcing calculator dates to 1975, with early uses by John Sherwood, Bayard Grimshaw, and Vic Perry.

(Thank you to Mark Strivings for help with crediting)