I'd probably charge less than you, so my ideas may be way out of sync with yours, but in a similar situation, I'd go for £50 a day, to be 'on standby', then charge a minimum of 2 hours normal rate for each call. e.g, £50 a day, even if you do nothing, then at least double your normal rate for a quick call-out. Anything more involved than a hour or so, I would likely charge at 1.5 times normal. I think this would be a reasonable rate for both sides, you will be compensated £50 a day for carrying around your mobile, and the Uni will not feel ripped off at paying those rates for the small chance of needing you. Alan.