'I'm sorry if I did something wrong,' said the girl meekly. Then Grandad said: 'Very clever, Princess. Roger was still working his line, but he was staring ahead with a thunderous expression. 'So it's just a name, going up and down all the time! Where's the sense in that?' Something was really wrong.

Just a name, no message or anything!' She had a sense that something was wrong, but she went on: 'I know a U at the end means it has to be turned round at the end of the line, and an N means Not Logged.' This was showing off, but she'd spent hours reading the cypher book. 'Yes, because it was a G code,' said Princess. He was always doing something in the tower when she was working the line, even though there was always a boy in the other chair. Grandad was the tower-master and had been everywhere and knew everything. Grandad had been hunched in the corner, repairing a shutter box in this cramped shed halfway up the tower.

'There was GNU, and I know that's a code, and then just a name. His hand didn't stop moving as he said: 'What did it say?'

It's Overhead, but it's in Plain.' On the other side of the tower, sitting in a seat facing the opposite direction because he was operating the up-line, was Roger, who was seventeen and already working for his tower-master certificate. It was very rare you got Plain in the Overhead.

It was instructions to towers, reports, messages about messages, even chatter between operators, although this was strictly forbidden these days. A lot of what travelled on the Grand Trunk was called the Overhead. See terrypratchett/ for more information.

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