how can you test for bugs in your excel spreadsheet

[Sybella]

I have 11 tabs and one cell seems to throw the totals out.  I cannot fathom out why this is happening.  There are no macros, just totals and sums on each tab that are linked to total tab.

[#2]

Thank you Joe User for your reply. Your reply was far too high brow for me but I managed to find the gremlin, just by deleting the cell and reentering the number. I am just glad that the numbers all tally now. I would love to know how to find the ISTEXT or ISNUMBER but given I have spent hours over the spreadsheet I think that is for another day!