Zero circle or circle of correction is defined as circle round the circumference of which if tracing point is moved, wheel will simply slide(without rotation) on the paper without any change in reading.
There are three methods of finding area of zero circle.
Method-I To find area of zero circle by using formula.
Area of zero circle =
Where, L= length of tracing arm from hinge to tracing point.
L1=distance from hinge to wheel.
R= length of anchor arm from hinge to anchor point.
+ve sign:- When wheel is placed beyond hinge away from tracing point
-ve sign:- When wheel is placed between hinge and tracing point.
Method-II To find area of zero circle by using planimeter.
i) Measure area of figure with anchor point outside of the figure.
ii) Measure area of figure with anchor point inside of the figure.
iii) Equate two results to find area of zero circle.
Method-III When constants M and C are known.
Area of zero circle = M × C
Where M= multiplying constant.
C= additive constant.