If the GIS coordinate system assigned to the drawing is not appropriate for the geographic location you set, measurements taken on the map may not be accurate.
Because the earth is not perfectly round, no single geographic coordinate system is able to accurately define all locations on the surface of the Earth. Consequently, various organizations define local coordinate systems, where measurements are taken locally from a local datum.
Local coordinate systems are considered more accurate because they align more closely with the Earth's surface in that locality, in comparison to an Earth-centric datum. Often, more than one coordinate system may cover the location you are interested in. As a general rule of thumb, the coordinate system with its datum closest to that location is considered to be the most accurate.
If measurements on the map are not accurate, change the GIS coordinate system of the drawing to a local coordinate system with a datum closer to your location.