I will try to Express what I said before in a different way which may be less obscure. It is very likely that the Romans (and whoever made that stone who was probably no more Roman than I am) wanted to represent something like "two long measures and one short measure." Quite a lot of our older measurement systems do that: miles, chains, yards, feet; gills, pecks, bushels and quarrers; stones and pounds and ounces. By having all these different categories you avoid fractions (and very large numbers) which arise if you try to express everything in a single unit. The decimal point is an evolution of the fraction, in many ways

So in short, the Romans avoided anything like a decimal point by using "mixed units" in measurements.