Look at this ascii art picture:

'Yeah', you say, and apart from the odd cryptic bit at the bottom, maybe you just think it says 'henry' in ascii art. Well pick up your monitor, flip it over on its top, and look again (or you could flip yourself over on your top). That's an ambigram. And so is the h2g2 logo (at least it is at time of writing).

Ambigrams seem to have been invented independently by a few people around the 1970s. Their first public appearance was in Scott Kim 'Inversions' (1981), followed by a walk-on part in Douglas Hofstadter's 'Metamagical Themas' (1985).

So how do you do them? Well the above is a rotational symmetry one, though you can also do them with various kinds of mirror symmetry, and even translational symmetry sometimes. This entry will concentrate on the rotational symmetry type.

The simplest way to do them, is to try to write the nth letter in such a way that the other way up, it looks like the nth letter from the end of the word. So in 'henry' above, the 'h' is written to look like a 'y' upside down. Many letter pairs work well here. For example, d-p, m-w, n-u, b-q, h-y and a-e. Note there are two ways in which 'a' is written: 'a' and 'a'. You want the one that looks like an 'e' upside down. If the two 'a's are not appreciably different, then you don't have the font 'Lucidia Sans' on your computer - the other way to write an 'a' is handwriting style - see the example below.

These letters work well with themselves: I, N, o, s, x, z. You can also make most letters look like themselves upside down, with a little tweaking. For example:

...are 'a' and 't'. But then you could see that anyway.

Sometimes matching single letters together doesn't work. No matter what you do, a 'm' isn't going to look much like a 'l' the other way up. Well have one large letter be more than one smaller letter upside down:

Hopefully you can see that is 'emily'. Here the 'm' is being the 'i', the 'l' and half of the 'y'.

As well as the 'a' and 'a' options, a few other letters can be written in more than one basic style, e.g. 's' (normal) and 's' (script handwriting style, again apologies if your computer doesn't have the font 'Lucidia Handwriting'), and many other variations on serifs and other twiddly bits/handwriting style effects can be useful in matching letters. Capitals give you more options too - though it does look a lot better if the capitalisation is correct for the word. For recognisability, the first and last letters are the most important to try to get looking right.

Sometimes there's a really horrible problem with an ambigram which isn't working. For example, it's pretty hard to get an 'O' to look like anything other than an 'O' upside down. Or double letters. Your brain automatically accepts a surprisingly varied selection of ways of writing a letter, but if you've got the same letter right next door in a different style, it doesn't like it. There are sometimes ways round double letters - use both of them in constructing some large letter the other way up:

... or just be lucky and find you can do them the same style. Some words just don't work at all - then sometimes you'll try it again months later and it all 'clicks' and people won't realise its an ambigram, at least until you turn it upside down.

That's about it for basics. Beyond here, mess about with words with pencil and paper, have a look at other people's ambigrams and always be on the lookout for any fancy ways to write letters.