With integers, besides adding and subtracting, it was easy to double and to multiply by 10:
Hydroxylic oxygen is obtained by subtracting the molecular refractions of acetic acid and acetaldehyde.
Since five Olympic periods have elapsed, the third year of the sixth Olympiad is 5X4+3=23; therefore, subtracting 23 from 776, we have 753, which is the year before Christ to which the foundation of Rome is referred by Varro.
Dates expressed according to this era are reduced to the common era by subtracting 5502, up to the Alexandrian year 57 86 inclusive, and after that year by subtracting 5492; but if the date belongs to one of the four last months of the Christian year, we must subtract 5503 till the year 5786, and 5493 after that year.
As the Syrian year began in autumn, the year of Christ corresponding to any year in the mundane era of Antioch is found by subtracting 5492 or 5493 according as the event falls between January and September or from September to January.