I've had this little program on my desktop for a while now, called Ratio Buddy, it helps work out the amount you need for pre-mixing the 2t oil and petrol ratio. Theres also some other interesting stuff on there that any tech-heads might take a liking to.
Ta! hope people find it useful, I know I have, also the enduro roll chart might be pretty usefull to some competition lads, I notice that the link is old, but If googled the freebie updated 3.0 version is about