Is it possible to define a function in Google Spreadsheets that can be used in any cell?
It would be helpful if I could define and use functions that refer to other cells in the same way that I can use native functions, e.g. by entering =myfunction(C1, C2, C3)
Yes – there’s a tutorial. Just use javascript functions by name in your spreadsheet. Define them using Tools > Script editor.
Watch out for name restrictions; I was confused by the behavior of functions that I created with names like “function x10() {}” not being found. Renaming to a longer name fixed it. There are probably documented rules for what isn’t allowed, but I don’t know where they are.