Enter the measured x and y values and the true x and y values into the calculator to determine the total variance from the true position.

## True Position Formula

The following true position formula is used to calculate the total variance from the true position.

TPV = 2 * SQRT ( (mX-tX)^2 + (mY-tY)^2) )

• Where TPV is the total variance from true position (this should be less than the total tolerance.)
• mX and mY are the measured x and y coordinates.
• tX and tY are the true x and y coordinates.

## True Position Definitoin

A true position is a type of geometric tolerance used to describe the true position of a feature with respect to 1 or more datums. For example, a hole position along the x-y plane.

## Can a true position be negative?

A true position cannot be negative. A true position is a measure of the absolute value of the variance of the position of a feature and such can only be equal to 0 at the very least.

## Does true position need a datum?

A true position should use a datum when used properly. The datum is usually referenced with x and y coordinates as the basic dimensions.

## Is a true position a radius of diameter?

A true position is most often described as a circle around a point with a certain diameter. For example, The true position with a tolerance of .010 would be a circle around the point with a diameter of .010.

## Does true position control perpendicularity?

When a true position is called out with datums on the face and sides of a part, the perpendicularity is also controlled by the true position. So in short, yes, the true position does imply perpendicularity when applied properly.

## How to calculate true position?

1. First, measure the values of the x and y coordinates of the actual part.
2. Next, determine the true values of the x and y coordinates outlined in the true position tolerance.
3. Finally, calculate the variance from a true position using the formula above.