Anyway, I found a handful of decent enough apps, all free. First up, the good people of Loughborough University, who have developed "Mathscard" apps which give formulae for GCSE and for A/As Level.
Yes, yes, I know this is not much cop for a Scottish curriculum, but a formula is a formula, at the end of the day. And did I mention the free bit?
Next - and very much for the lower end of the market - comes a company calling itself Maths Tappers. Hmm. They have a few free apps to play with but the one that caught my eye is their "equivalents" app, which gets pupils to match fractions and percentages.
In my experience, the more practice pupils get at this sort of stuff, the better. You bet your life I'll be recommending the hell out of this one to all and sundry.
Now, is it still raining...? Yeesh.