What’s the nitty gritty part of this? Putting down the code. So [laughs] putting down the code, lots and lots and lots of cord, and checking, and checking, checking, flow chart against code, code against flow chart. And in our case always having a second party checking the code against what is specified, which is the floor chart, but very rarely checking the floor chart against the original specification. So that’s another possible source of error. But it is putting down code, and improving that code as you go through. And testing, testing, testing. Again, one of the skills is devising the testing, as you heard, how do you make as comprehensive a test as you can do? It means thinking of all the events, the most unlikely events, which may not ever have occurred, but could conceivably occur. In the LEO case, having had a second person check it, you then put it into computer form, in our case in punch cards. When you were testing a programme, you worked with an operator on the computer; you handed the operator the programmes, you worked with them then as the programme was tested. And we had the facility for single stepping for the programme so, if you had a problem, you could single step and see where things were going wrong. Once these rows of blips, the blips, blips were the binary, so you would see nothing, nothing, blip; nothing, nothing, blip, blip, and so on. But this was not encouraged because we were told that it was a failure if you had to do that - we should go on clean. But of course we never quite did.