I am trying to get my arms around a problem of size. I have a large spreadsheet (2,000+ rows and about 250 columns). The entire data area is formulas which derive inputs from a separate tab in the same workbook. This spreadsheet is used by several users. I am trying to write a utility which can check for consistency of formula in each row. To describe it better, the program should:

1. Check whether the formula in a cell is identical to the cell on the left (Therefore, if there is a hard coded value across any of the 250 columns, it represents an inconsistency. Similarly, even if its a formula, the formula cant be different. For example, if cell A5 has $A$1*B1, then cell B5 cannot have B1*C1 (instead it should have $A$1*C1)

2. It should be able to highlight/identify cells with identify/perceived errors (as set out in the examples used in point 1 above)

The following are the restrictions:

1. Locking the sheet (or making it read-only) while otherwise providing a sensible alternative, is not an option in this case.
2. Since multiple users use the file, this is required to guard against inadvertent keystrokes, mouse drag-and-drops or just experimentation which the user does not "undo" but rather saves changes before closing
3. It is safe to assume that the formula in the first column does not get edited at any point (to avoid greater complexity in the code)

Thanks in advance