help needed

Would really appreciate it if anybody could help with the following:

Have purchased a number of shares in the same company over the last year. Have also sold a number of shares in the same company over this period. However, the average unit cost that I come up with after deducting the sale of said shares, is more than that shown on my Westpac trading account. I have been over my figures several times but am unable to reconcile the difference. Does anyone know of a simple spreadsheet that I can download, whereby you input all your buy and sell figures, and it calculates the average unit cost for you. I'm pretty sure I haven't made any errors and am using the FIFO rule. Any help with this would be greatly appreciated because its driving me mad, and if my figures are wrong, I'll effectively be better off than I had thought!!