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True position calculator

True position is twice the radial distance from nominal: TP = 2·√(ΔX² + ΔY²). A hole measured 0.05 mm off in X and 0.03 mm off in Y sits at a true position of Ø0.117 mm. Enter your measured deviations, and — if the callout carries Ⓜ or Ⓛ — the actual feature size, and the calculator adds the bonus tolerance the departure from MMC/LMC earns before giving a pass/fail against the frame.

Measured deviations

Optional — spherical (SØ) zones only

Optional — enables pass/fail

Enter ΔX and ΔY deviations to compute the position. Add the tolerance for pass/fail, and choose MMC or LMC to include bonus tolerance.

Position = 2·√(ΔX² + ΔY²[ + ΔZ²]). At MMC or LMC, bonus = departure from the stated material-condition boundary, and allowed = stated tolerance + bonus (ASME Y14.5 position at material condition).

Symbols and modifiers: GD&T reference.

Derived

Computed from the standard true-position formula (2·√(ΔX²+ΔY²)) and ASME Y14.5 MMC/LMC bonus-tolerance principles

Values follow the governing standard, which is authoritative for production and inspection decisions. Verify against it before you rely on a number.

Standard names are trademarks of their respective owners; ASdrawn is not affiliated with or endorsed by any standards body.

Where does bonus tolerance come from?

At maximum material condition, a hole at its smallest allowed size gets exactly the stated tolerance. As the hole is made larger (toward least material), the extra clearance becomes usable position tolerance — the bonus equals the departure from MMC. That is why an out-of-position hole can still pass: the frame's Ø0.25 Ⓜ may effectively be Ø0.31 for the hole as made.