Units of measure — Stored once, in one unit

A Number or Currency column can declare a canonical unit — the unit its values are held in. Type 1200 g into a column held in kilograms and 1.2 is what lands in the cell. The conversion happens once, at the moment of writing, which is what lets everything downstream stay simple: a total is a total, a filter is a comparison, an export is a number a spreadsheet will accept. What you typed is kept. The entered value and its unit ride alongside the stored number. Reopen the cell and it offers back 1200 g, not 1.2; the cell's tooltip says Entered as 1200 g. So a column can be filled by five people using three different units and still be one clean set of numbers, without anyone losing their own record of what they wrote.