Comparing the Elliptical and Automatic Area Measurement Tools

If you measure a circle (or any other shape) with , it will count how many pixels are in the area with similar colors.
But if you measure the same circle or ellipse with , it will calculate the number of pixels by using the following mathematical formulas:

Circumference Area = Pi * (diameter/2)^2
Elliptical Area= Pi * (diameter a/2) * (diameter b/2)

Although both tools will do the measurement correctly, they will give slightly different areas because one of them is using a mathematical formula, but other one is counting real pixels.

Both measurements will be valid, but they cannot be compared between them nor mixed when evaluating series.