I assume your circle is not on the Y axis. So for the radius you must enter a relative coordinate for the point on the circle.
When the center is set, enter
@.3125,0 or
@0,.3125 or
@.3125<45.
The last one means move .3125 relative to the center at an angle of 45° and this would work with any angle for a circle.
You can even enter formulas for coordinates, e.g. use the diameter and avoid to miscalculate the radius
@.625/2<45Another option is to use the Circle/Radius tool. With this tool you have to enter the radius in the appearing field of the tool option bar (above the drawing area).
Even there you can enter
.625/2 for the radius.
This tool is handy when you have to draw many circles with same radius.
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