In early Egyptian and Greek mathematics, unit fractions were generally the only ones present. This meant that the only numerator they could use was the number 1. The notation was a mark above or to the right of a number to indicate that it was the denominator of the number 1. The Romans used a system of words indicating parts of a whole. A unit of weight in ancient Rome was the as, which was made of 12 uncias. It was from this that the Romans derived a fraction system based on the number 12. For example, 1/12 was uncia, and thus 11/12 was indicated by deunx (for de uncia) or 1/12 taken away. Other fractions were indicated as : 10/12 dextans (for de sextans),

3/12 quadrans (for quadran as)

9/12 dodrans (for de quadrans),

2/12 or 1/6 sextans (for sextan as)

8/12 bes (for bi as) also duae partes (2/3)

1/24 semuncia (for semi uncia)

7/12 septunx (for septem unciae)

1/48 sicilicus

6/12 or 1/2 semis (for semi as)

1/72 scriptulum

5/12 quincunx (for quinque unciae)

1/144 scripulum

4/12 or 1/3 triens (for trien as)

1/288 scrupulum

Today we write out 1999 in Roman numerals as MCMXCIX and to perform any arithmetical operations with theses numerals is almost impossible.

However. the Romans themselves would have calculated the equivalent of 1999 on an abacus counting device as MDCCCCLXXXXVIIII and by placing I to both sides of these numerals simply wrote them out as IMM (-1+2000=1999)

A quarter of 1 is 1/4 which is the equivalent of :. as a Roman fraction because a dot or a dash represented 1/12 and :. is 3/12 which is a 1/4.

So it follows that a quarter of IMM would probably work out as :.D (-0.25+500=499.75) which is a simplification of CCCCLXXXXVIIIIS:. (499.75)

Roman fractions . is 1/12, : is 2/12, :. is 3/12, :: is 4/12, ::. is 5/12, S is 6/12, S. is 7/12, S: is 8/12, S:. is 9/12, S:: is 10/12, S::. is 11/12 and SS = 12/12 = 1

In Roman times there were 12 uncias to an as and 16 asses to a denarius from whence evolved our modern words for inches and ounces

In his fascinating reference book about early numeration systems entitled 'History of Mathematics' volume 2 by David Eugene Smith first pubblished in 1925 and ISBN 0486 204 308 he gives thorough details of how Roman numerals and fractions were once worked out.