With the "radius" dimension
we're going to measure the "radius" of a circle or an arc.
Draw a circle of radius 50 after which, activate the dimension "radius".
At this point, clicking anywhere on the circle will appear as the dimension in the previous cases and it will follow the mouse movement to determine the final position which may be inside or outside the circle.
We will then clicking again to place the dimension and exit the command.
The radius value on the dimension, will be preceded by the word "R" to highlight it.
, in a totally equal to the command radius, mark it the diameter of a circle or virtual diameter of an arc.
The value of the dimension will be preceded by the symbol Ø.
Make some tests, by dimensioning a circle with radius and diameter and placing the dimension inside and outside of the circle to see how they are represented.