Returns the sheet number, given a reference.
- returns the sheet number of reference, where reference is a reference to a cell.
- If reference is omitted, the sheet number of the current sheet (containing the formula) is returned.
- returns 2, if you have 3 sheets - Sheet1, Sheet2, Sheet3 - in that order, because Sheet2 is the second sheet.
- returns the current sheet number (of the sheet containing the formula).