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Roman numerals and clock faces

Friday, 22 February 2013

I’ve recently been working with teachers at The Green Way Academy Hull, sharing ideas to develop their maths planning.
Earlier this week I was lucky enough to be in a Y3/4 shape lesson which used ‘The Romans’ as a context. It was really creative, with children tessellating regular shapes with the aim to design a tiled pattern for a box they will make to hold a Roman artefact. I’m looking forward to seeing the end results.

The Ancient Romans as a theme offers such a rich context for mathematical starting points. The new NC Programmes of Study includes reading and using Roman numerals, which would obviously fit in, but seems typically knowledge and fact based.

Going a little deeper into reading and writing Roman numerals, and it is a fascinating historical number system. Time to explore it may be an issue, so, as a minimum, it will involve children from Y4 onwards in:

•  putting Roman numerals in a historical context (that could be an interesting week long topic in itself)

•  understanding that symbols in each number are placed in order of value, starting with the symbol of greatest value, and that adding the value of the symbols will give the total number.

•  knowing the exceptions to the rules; that if a lower value symbol appears before a larger value symbol it is subtracted not added.

XI is 10+1=11                                    IX is 10-1 = 9
XVI is 10 + 5 + 1 =16                        XIV is 10 + (5 -1) = 14

Roman clockface

Is it III or IV ? The mystery of clockfaces

There is an interesting everyday exception to the conventional rules for Roman numerals when written on clock faces.

Try this activity when exploring Roman numerals:

Show some pictures of different clock faces with Roman numerals.

Ask the class why they think the symbol for 4 is IIII rather than the conventional IV.

Give them the following possible reasons, perhaps on card or up on the interactive whiteboard. The children can debate the choices and decide on one, or suggest a different possibility.

The IV may be confused with the VI if it was used when reading the time.

IV was avoided because it represented the Roman god Jupiter, whose Latin name IVPPITER begins with IV
Louis XIV, King of France, preferred IIII to IV and ordered clockmakers to use this form to show the numeral on clocks
The I symbol is all that is used for the first four hours, The V symbol is used in the next four hours and the X symbol in the last four hours. This makes a pleasing pattern.
It looks more symmetrical and balanced with the IIII and VIII both having 4 characters

Did the class manage to agree on one choice?

There is no definite correct answer, it is not known why IIII was used rather than IV.  A lack of evidence is often a problem with history – and historians have to find the most likely explanations.

I personally like to think that it’s the use of I, V and X in each block of four hours – just because I like a good pattern!

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