Groupon coupon confusion… HOW much?!

A recent Groupon discount offered ‘up to -70%’ discount on eating out.  Note the minus…

Up to minus 70%? What’s that then?

I guess they mean you can get up to 70% off the normal price. But the minus bit makes things pretty confusing, especially if you know anything about maths.

‘Up to minus 70%’ actually means a discount of anything between minus infinity and minus 70. Work that out in pounds and pence if you can.

‘Up to’ isn’t a very good offer anyway, even when you don’t include negative values. Up to 70% translates as anything from nought percent to 69%. Which might or might not be a good deal. So could easily disappoint people who don’t get the full 70% discount.