## Friday, 4 March 2016

### Roman numerals

Here are three questions about Roman numerals that genuinely puzzle me!
First, why, in the twenty-first century, do we persist in using Roman numerals in particular contexts, such as the hours on clock or watch faces, and dates on buildings or at the end of a movie?
Second, in such a technological age, can anyone really justify the inclusion of Roman numerals in the statutory English primary mathematics curriculum and in the associated national assessment of mathematics?
Third, there’s something odd I’ve noticed recently about Roman numerals on clock and watch faces. It is important for teachers to be aware of this, because there are limited contexts for assessment items in Key Stage 2 national mathematics tests in this country, so clock and watch faces with Roman numerals turn up often.
In an early form of Roman numeration, the numbers we call ‘four’ and ‘nine’ would be represented by IIII and VIIII. A later development was to represent these more concisely as IV and IX, the convention being that when a letter representing a smaller value is written in front of another letter, then the value is to be subtracted, not added. So, XC would represent 90 (100 subtract 10). So, here’s what we have noticed: in most cases where Roman numerals are used on a clock or watch face, the four is written using the early system (IIII) and the nine is written using the later system (IX). Check this out and see if we are right. The question that puzzles me is, simply, why?

1. Hello Derek. I've just recently found this blog! So hello again.

Fascinating post. I can only count up to 12 in roman numerals which is a bit of a disadvantage as I dabble in church history and can't read dates in churches! I suppose I ought to sit down and do some work on the subject!

The preference for Roman numerals might be connected with the upper class snobbery that revolved round being initiated into the classics. However I must admit that Roman numerals on a clock give it that air of settled establishment and stability especially if the clock is in some olde worlde or government building.

I had a look at my sun dial and sure enough the 4 was written as IIII and the 9 as IX. The only light I can throw on it is that on my sun dial there would barely be room for VIIII. But then IV is shorter than IIII. The following web site doesn't seem to have a definitive answer either: http://mentalfloss.com/article/24578/why-do-some-clocks-use-roman-numeral-iiii

1. Good to hear from you, Tim!

2. I agree with you about including them in the statutory curriculum. I did however include them in a unit on how we write numbers that seemed to go well:

http://followinglearning.blogspot.fr/2016/01/how-we-wrote-numbers.html

3. Thanks, Simon. You are right in reminding us that there is value in discussing with children the contrast between the system of Roman numerals and the Hindu-Arabic numeration system that we use today. This is, of course, that Roman numerals do not use the concept of place value. 'V' represents five wherever it is written, for example. It is always good practice in teaching to reinforce a concept or principle with some non-exemplars!