Pentax R-200 Series Instruction Manual page 114

Input H. angle and press [ENT] to view the RESULT OF COORD. CALCULATE screen.
The second point Coordinates are displayed by plus or minus from the known Coordinates.
Press [ENT] to view the following screen.
The PN, X, Y, Z and PC are viewed and can be edited.
If all items are OK, press [F5][ACCEPT] to save them.
8.1.3 CIRCLE RADIUS
The center point and radius of the circle drawn by three points are calculated by this function.
You can store calculated center point.
Input: 3 points
Output: Center point of the arc
Radius of the arc
From the PowerTopoLite screen, press [F2][CALC] to view the CALCULATION screen.
P2
P1
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P3
Center P
Radius