Baudot

Five bits give thirty-two combinations, which will not hold the letters and the digits at once. So two of the thirty-two are shifts. LTRS and FIGS decide which of two meanings the other thirty carry, exactly like holding down a shift key, and a teleprinter sent one only when the mode had to change. It also meant that a telegram which dropped a single character could come out as gibberish for the rest of the line.

This is properly ITA2, the International Telegraph Alphabet No. 2 of 1924. Emile Baudot’s own code of 1870 was a different arrangement, but his name stuck to the idea.

Coldplay’s X&Y sleeve is this code. Each column of colour blocks is one five-bit character - a block for 1, a gap for 0 - and the colours themselves carry nothing at all. The title is three characters but the sleeve has five columns, because the ampersand lives on the figure shift and so needs a FIGS before it and an LTRS after it to get back to the Y.

Examples:

Bit 1 goes down the wire first and so is written leftmost, which is the reverse of how the code’s value reads. That is where hand-copied versions of this table usually go wrong; the published values for the sleeve, X = 10111 and Y = 10101, are what pin it down.

The figure shift here is the American teleprinter arrangement, which is the one with the ampersand on it. International ITA2 puts a pound sign where the hash is, a plus where the quote is, and an equals where the semicolon is.