Gill
Just to come at this from a different angle, most online bookies also quote prices in decimal format you just need to find the button. This would eliminate the need for all that excel jiggery pokery!
Are you looking at arbitrage? It has something that has caught my eye a few times in the past. I used to have loads of spreadsheets that could analyse various events but since I upgraded my computer I haven't got them anymore, sorry.
Good luck
Saint