The rms display appears only when the checked mean square has an exact root. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Rms is shown only when exact
A mean square of 9 square metres has exact rms 3 metres.
9=3
No approximate square-root label appears
The scene can display rms 3 because the square root is exact.