Hi and thanks for all the replies !

I found it a bit stranghe though and very costly for the underground to
actually built 3 trains for the public to choose.

Usually companies (like Bus companies) choose the model themselevs then they
buy few dozens of them they wopuldnt actually built 3 different busses and then
get rid of them

I dont know just sounds abit strange and indeed for the rest of the new trains
of the underground (waterloo/northern) they didnt have any prototype trains

you guys agree with me ?

cheers