I'm just looking at a drawing of a sheet piling layout. It has dimensions on it, for example 6670.052. The units are millimetres. This means what ever it is is being measured to the nearest 0.001 mm . That's 1 micron. Human hair is 70 microns. Joe average bacteria are 1-2 microns diameter. Sheet piles (GBFO lumps of steel) are not manufactured to such tolerances.