# Blog

## Archive

Show me a random blog post**2019**

**2018**

**2017**

**2016**

**2015**

**2014**

**2013**

**2012**

## Tags

sorting video games wool ternary accuracy sound hexapawn menace harriss spiral arithmetic folding paper propositional calculus graph theory raspberry pi reuleaux polygons news bubble bobble curvature royal baby chess braiding radio 4 misleading statistics countdown golden spiral php people maths fractals geometry statistics binary folding tube maps asteroids javascript puzzles matt parker frobel map projections rugby inline code electromagnetic field christmas card london underground mathsteroids the aperiodical trigonometry aperiodical big internet math-off national lottery game of life dates data craft light reddit machine learning sport books latex captain scarlet dataset plastic ratio speed cross stitch martin gardner manchester flexagons platonic solids game show probability games python christmas tennis manchester science festival approximation world cup weather station coins noughts and crosses hats nine men's morris chalkdust magazine a gamut of games triangles pac-man draughts european cup dragon curves realhats bodmas pizza cutting gerry anderson pythagoras interpolation probability final fantasy mathslogicbot palindromes chebyshev polynomials stickers logic go rhombicuboctahedron estimation golden ratio error bars london oeis programming twitter football**2014-03-19**

Vending machines identify coins by measuring their width. Circular coins have the same width in every direction, so designers of vending machines do not need to worry about incorrectly rotated coins causing a blockage or being misidentified. But what about seven-sided 20p and 50p coins?

Perhaps surprisingly, 20p and 50p coins also have a constant width, as show by this video. In fact, the sides of any regular shape with an odd number of sides can be curved to give the shape a constant width.

Today, a new 12-sided £1 coin was unveiled. One reason for the number of sides was to make the coin easily identified by touch. However, as only polygons with an odd number of sides can be made into shapes of constant width, this new coin will have a different width when measured corner to corner or side to side. This could lead to vending machines not recognising coins unless a new mechanism is added to correctly align the coin before measuring.

Perhaps an 11-sided or 13-sided design would be a better idea, as this would be easily distinguishable from other coins by touch which being a constant width to allow machines to identify it.

### Similar posts

The end of coins of constant width | New machine unfriendly £1 coin, pt. 2 | World Cup stickers 2018, pt. 3 | World Cup stickers 2018, pt. 2 |

### Comments

Comments in green were written by me. Comments in blue were not written by me.

Add a Comment