This simple procedure can be repeated again to determine further points on the arc, as follows....
A new fixed point on the arc has now been established at point D. A new chord can be created between A and D, and, when measured, this is found to be 1662mm in length.
The midpoint of this new chord can be determined by measuring from A (or D) and then labelled as (E). This creates a yet another rightangled triangle AER and it has already been noted that AR=1800mm and we can calculate that AE= half of 1662mm = 831mm. Using Pythagoras...
RE = SQRT (AR²  AE²)
therefore,
RE = SQRT(3240000  690561)
= SQRT (2549439) = 1597mm
