Non Librecad DWG file has wrong dimensions when opened in LC

I have a whole set of house plans created twenty years ago on a long-forgotten cad system that are in DWG format.  I can open the DWG files in Librecad 2.1.3.  When I use the dimension function in Librecad, the dimension numbers are wrong.  

Example, for a line in the DWG file that measured 100cm, the Librecad dimension function shows the line to be 110cm.

My question is what do I do in Librecad to change the DWG file so the dimensions generated in the Librecad dimension function  match reality.

If the line measures 100 cm with the measuring tool, it means it is really 100 cm. You can manipulate the reading of a dimensioning in Options - Current drawing preferences - Dimensions - Length factor. Normally this should be 1. Maybe it is set to 1.1 by some reason, or, if it's properly 1 the dwg is somehow queer and you can correct the reading with 100/110.