I normally open a new from scratch in metric or a template that are in metric, make sure Space Unit/ Presision is at min 6 for accuracy.
Make sure the scale is 1:1
Then insert the drawiing and make sure the 2 checkbox at the rigth side is checked (convert and override) in menu when doing so.
Then the scalefactor is 1/ 25,4 = 0,0393700787401575
Then Select everything in the drawing ( ctrl + A)
Past 0,0393700787401575 in to scale x and y as it is a 2D drawing and hit enter
In this drawing they have scaled it to fit a paper in 1:100 so it is 1:98, something, so make sure its 1:1 in Space Units afterwards
Find a long measurement to check, i used the 16100 at the top in this drawing, make a Ortho Dimension on the same place/ points, and the result should be 16100, the fun thing is that the original measurement is not a Dimension in TC, but text, maybe it have been exploded or similar at a point.
V20, V21, 2015/ 16/ 17/ 18/ 19 Pro. Platinum
Deluxe 2015/ 16/ 19
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB