The first of the month is a good time to note down this little trick for spreadsheets:

`=sumif(B1514:B1543,"<>",C1514:C1543)`

This is useful in the solar generation spreadsheet I run, since it sums in column C only when there’s a value in column B; the near–OCD spreadsheet has running calculations in place that make this better than daily editing of the total at the monthly termini in column C (itself a collection of differences).

e.g. C1543 : `=B1543-B1542`