Hi Michael,
The scale bar should always shows the correct scale ratio of the map in a viewport. When the viewport scale was changed, the map scale was changed accordingly, in that case we have to adjust the scale bar. Here we have two choices, one is to adjust the scale bar size and keep the division value unchanged, another is to change the division value and keep size unchanged. This is configurable in “Scale bar properties…” dialog, the “Adjust divisions on zoom” checkbox.
For example, we have a map scale 1:10000 and viewport scale is also 1:10000 (viewport scale can be different from map scale), we want a scale bar shows 1:100Meters, then division value is 100.
If viewport scale was changed to 1:20000, then scale bar size is doubled in order to keep division value (100) unchanged.
If we check “Adjust divisions on zoom”, then scale bar size won’t be changed, the division value will become 50. Because the same division size presents ½ original map distance now.
Hope this will help!
Tatiana Machado
AEC-ENI Application Engineer