Variations in graphic scales

[CT_GIS]

Hi,

See below the scales created for two maps.

Why do they generate with slightly different scale bars?

Also, checking the ratios of length in CM / miles does not yield the same ratio between maps (2.4886/45 is not close to 2.4996/55)

It would therefore be inaccurate to use the same graphic scale bar on both maps, right?

I am extremely appreciative of any assistance from the Esri team and community. 

[CT_GIS]

another example comparing graphic scales from two maps at a higher detail.