A great post over at TZ-UK which makes the point that the when we talk about the differences in size between say a 36mm watch and a 39mm watch, we often underestimate the size difference. Simple maths would say that the 39mm watch is 9.2% bigger than the 36mm..but that's not really the case.

At the back of your head, you'll remember that the area of a circle (or dial) is πr^2, so the difference in area between a 36mm dial and a 39mm is actually 17%. The table below from the TZ-UK post shows the percent larger or smaller different watch diameters are from the base 36mm (Carrera Re-edition)

Diameter Area Percentage
32 ........... 804 ......... -21%
34 .......... 908 ......... -11%
36 ......... 1018 ......... 0%
39 ......... 1195 ......... 17%
40 ......... 1257 ......... 23%
42 ......... 1386 ......... 36%
43 .........1452 ......... 43%
45 ......... 1591 ......... 56%
50 ......... 1964 ......... 93%

Thought that was a good reminder that size matters!