Currency hard to get head round

It's not just UK tourists who struggle to understand exchange rates between the Pound and other currencies, even one as widely used as the Euro.

http://news.bbc.co.uk/2/hi/europe/7146650.stm
Spanish Economy Minister Pedro Solbes says:

"I see people having a couple of coffees and calmly leaving a euro tip,"

"That's 50% of the value of the product."

Before the euro hit the streets five years ago, leaving a 25 peseta tip was the norm. One euro was then worth 166 pesetas.

In the UK a tip of 10% is fairly standard - so how much do you tip and do you understand the exchange rate?
Currently £100 is about €139 but the rate does vary and this is what probably confuses people.
On a bill of €10 you could tip €1 and that would be fine.
Think of it as a percentage of the bill rather than trying to work out how much it'd be in English money.

If currency conversions off the top of your head aren't your thing then write a list out at the time you go on holiday showing you how much £1, £10, £50 and £100 is. Write it on a small bit of card and put this in your purse. That way you can look at it before paying out any money!