Off-the-shelf Masterclass: Digital Computers

Off-the-shelf Primary Mathematics Masterclass about the art and science of counting on fingers. Since ancient times, humans have used their fingers for counting and calculations.

Learn about ways you too can become a ‘digital computer’ and find out about binary numbers with the demonstrations and activities in this session.

  • Credit: Ibex73 via Wikimedia Commons

About this Masterclass

Historically, fingers have always been used for counting. In fact, a standard pair of human hands with 10 fingers forms the basis of our decimal number system. Other systems include the modern hexadecimal, with base 16, and the historical vigesimal system used by the Ancient Mayans with base 20. One of the most important number systems is binary - a counting system at the heart of modern-day computers.

Counting on your fingers can be achieved in many ways - the ‘thumb first’ system is claimed to be widespread in continental Europe, while starting with the index finger is supposedly more popular in the UK and North America. 

Through the demonstrations and activities in this session, students will learn about ways that they too can be ‘digital computers’, magicians and binary decoders.

Length: 2 hours (see the session leader notes for ideas on how to shorten the Masterclass).

Resources needed

  • Post-it notes cut into strips (for students to wrap and stick around fingertips) 
  • Mind reading cards (printed from worksheet)
  • Converting between binary and decimal worksheets - two sheets, one each per student
  • ‘Counting in binary’ cheat sheet with fingers needed shown - as need
  • Computer and data projector
  • Optional extra: Writing your name in binary worksheet - one per student
  • Further details of quantities etc. can be found in Session Leader Notes


All supporting notes, worksheets and solutions can be downloaded from this page along with the Powerpoint presentation.

The Session Leader Notes offer full notes on the activities and a detailed list of resources, including quantities needed. For additional guidance, the session script gives a full run-through of the Masterclass.

The Session Helper Sheet can be distributed amongst helpers and an Additional Information Sheet giving more details on the history and background of the subject is provided for added interest.

Ask the Ri

You can collect any student questions and email them to the Ri Masterclass team at - we will endeavour to answer them before the next Masterclass in your series.

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