A centimetre is 2.54 inches. At Giza, the number 254 is found as a factor which links various linear dimensions. What does it mean to multiply or divide a linear measure by 254? What does it mean to convert inches to metres, or vice versa?

254 is not the only factor that links the key dimensions at Giza, but it is a common theme. The other factors seem to be based in geometry (such as π , √3), and astronomy (such as 223, 235 and 29.53059).

As 29.53059 x 4/3 inches are close to 10 000 / 254 inches, as are 365.242199 / 354.36708 x 100 / 2.61803 inches, they can be used almost interchangeably to interpret the dimensions at Giza.

10000 / 254 = 39.3700787402

29.53059 x 4/3 = 39.37412

365.242199 / 354.36708 x 100 / 2.61803 = 39.368871

The number 254 is linked to both astronomy and geometry. It is linked to pi, to Phi squared, and to the solar and lunar years, as well as being the number of sidereal months in a Metonic period.

When linear dimensions at Giza are multiplied or divided by 254, it's not necessarily that in one place inches were used and in another metres were used. The metre and the inch can both be said to co-exist at Giza, and even if the metre hadn't appeared in the 18th century it would still appear at Giza. But the use of 254 could in fact be a reference to the ratio between the solar and lunar years combined with Phi squared, or to pi divided by the mean number of lunations in a year.

If we think of possible links between the metre, the inch and the Egyptian royal cubit, the number 254 also makes an appearance, since 2.54 cm are an inch. Converting between inches and metres allows us to see ways of thinking about the Egyptian royal cubit, in relation to geometry and astronomy.

The links between these three units, inch, metre and cubit, and to astronomy and geometry, may hint at something of the symbolic and religious significance of the cubit in ancient Egyptian cosmology and astronomy. It could also explain some of the enduring appeal of the metre and the inch.

Another interesting connection to be made to the number 254 is that, as Howard Crowhurst points out in his book Carnac the Alignments, there are 127 kerb stones around the base of Knowth, in Ireland.

The presence of the number 127 in Ireland seems to suggest a link to the repeated presence of 254 at Giza. The 127 stones at Knowth also suggest we should take the inch - metre connection seriously when analysing ancient sites.