A spreadsheet is a program that allows storing data and formula in tables of rows and columns. Some examples include Microsoft Excel, Lotus 123, Quattro Pro, and

Google Spreadsheets. (The term came from the practice of using large sheets of paper marked with grids, for financial calculations, but that meaning is mostly obsolete now.)

For example, to calculate Roman lengh units, you could create a spreadsheet with these formula (dividing columns with the | character):

Row A: 'Input | 'Unit | 'Mille | 'Passus | 'Gradus | 'Pes | 'Uncia

Row B: (empty) | 'Mille | =B1 | =B1*1000 | =B1*2000 | =B1*5000 | =B1/60000

Row C: (empty) | 'Passus | =C1/1000 | =C1 | =C1*2 | =C1*5 | =C1*60

Row D: (empty) | 'Gradus | =D1/2000 | =D1/2 | =D1 | =D1*2.5 | =C1*30

Row E: (empty) | 'Pes | =E1/5000 | =E1/5 | =E1/2.5 | =E1 | =E1*12

Row F: (empty) | 'Uncia| =F1/60000 | =F1/60 | =F1/30 | =F1/12 | =E1

Someone using such a spreadsheet could fill in an empty spaces, and the spreadsheet program would display the calculated values in the other cells of the same row. For example, if I filled in the empty space in row E with the value 50, the spreadsheet program would automatically calculate the values 0.01, 10, 20, 50, 500 for the other columns (ignoring the second column, which would remain "Pes"). If I changed the number to something else, the spreadsheet program would automatically recalculate the new values for the other formula spaces.

(Forgive me if I have messed up the units. I found a site that says there are 1000 Passus per Mille, 2 Gradus or 5 Pes per Passus, and 12 Uncia per Pes. I know I'm using only the singular words for the units, and that I should be using plurals.)