06/05/2026
1. What is True Position?
True Position tells you how far a feature (like a hole) is from its ideal (theoretical) location.
* It controls location in both X and Y directions
* The tolerance zone is circular (not square)
๐ Think: โHow far did my hole shift from where it should be?โ
โธป
๐น 2. Basic Idea (Visualization)
* The exact location = center of the circle
* The actual hole location = somewhere inside or outside
* Allowed area = circular tolerance zone
If the actual point lies inside the circle โ OK (PASS)
Outside โ NOT OK (FAIL)
โธป
๐น 3. Formula Used
TP = \sqrt{(\Delta X)^2 + (\Delta Y)^2}
Where:
* ฮX = difference in X direction
* ฮY = difference in Y direction
๐ This is basically Pythagoras theorem (distance calculation)
โธป
๐น 4. Example from Image
Nominal (Target):
* X = 10.00 mm
* Y = 25.00 mm
Measured (Actual):
* X = 10.08 mm
* Y = 25.13 mm
Deviation:
* ฮX = 0.08 mm
* ฮY = 0.13 mm
โธป
๐น 5. Calculation
TP = \sqrt{(0.08)^2 + (0.13)^2}
= \sqrt{0.0064 + 0.0169}
= \sqrt{0.0233}
= 0.15 \text{ mm}
โธป
๐น 6. Tolerance Check
* Given tolerance = ร 0.5 mm
* Radius = 0.25 mm
๐ Condition:
* If TP โค 0.25 โ PASS
* If TP > 0.25 โ FAIL
โธป
๐น 7. Final Result
* Calculated TP = 0.15 mm
* Allowed = 0.25 mm
โ
PASS (within tolerance zone)
โธป
๐น Key Takeaway (Very Important)
True Position is:
The straight-line (radial) distance between actual and theoretical position
