Sensible Train-Spotting

A small man in an anorak with a Thermos flask sits on a bench by some busy
train lines and notes down the train numbers as they go.

All the joy (?) of trainspotting but from the comfort of your computer, your
task is to tick off the numbers of various trains as you see them come past
your position. The game difficulty increases as you progress, to a point where
there are 16 train numbers to tick off and five train lines in front of you,
with everything masking everything else.

Sensible Train-Spotting