not by five to ten millimetres, but by 200 to 400 millimetres, which is substantial. apart from mistakes and misinterpretations, there are many decent reasons why building work may have to deviate from the plans, depending on the realities of the environment. but the important thing is for a construction manager to be able to walk the site and spot those deviations and decide whether they or the plans need fixing. hang on, we've got another pipe problem. look. right, there's another pipe that's supposed to be going that way, and they made it go that way. there is a pipe that's supposed to be going there, and it's not. it's not here at all. exactly. well, they forgot to put in a pipe. 0r there was a change made on site where they decided to go outside. once this is handed off to the next trade or the next set of work starts, because that has a knock—on impact on the rest of the building process.