How this true position calculator works
For each feature, the worksheet subtracts the basic coordinate from the measured coordinate to get ΔX and ΔY. The radial center error is √(ΔX² + ΔY²). A circular position tolerance is reported as a diameter, so the displayed true position is 2 × √(ΔX² + ΔY²).
Do not enter bilateral coordinate tolerances as the position callout. Enter the diametrical tolerance shown in the feature control frame and coordinates measured in the datum reference frame established by the drawing and inspection method.
RFS, MMC, LMC, and feature bonus
RFS applies the stated position tolerance without a size-derived bonus. For a hole evaluated at MMC, the smallest permitted diameter is MMC and growth away from that size adds an equal amount of bonus. For a pin, the largest permitted diameter is MMC and reduction from it adds bonus. LMC reverses the controlling size direction.
The tool always checks actual size separately. A feature outside its size limits fails overall and earns no displayed bonus, even if its coordinate result alone would fit.
Important scope boundary
This is an arithmetic inspection worksheet, not a complete GD&T conformance engine. It evaluates each entered feature independently. It does not establish a datum reference frame or calculate datum feature mobility/shift, simultaneous requirements, composite position, pattern translation or rotation fitting, projected tolerance zones, orientation, surface extraction, uncertainty, or CMM strategy. Do not add datum shift to the entered position tolerance unless a qualified procedure has already established how it applies; this tool deliberately does not guess it.
Inspection workflow
- Confirm the drawing revision, units, feature type, size limits, position modifier, and diametrical callout.
- Establish the specified datum reference frame with the appropriate physical or software method.
- Export basic X/Y, measured X/Y, and actual feature size from the inspection record or CMM report.
- Paste the six columns, inspect every highlighted failure, and retain the exported CSV with the source measurement record.
- Have qualified inspection personnel resolve datum, composite, pattern, or uncertainty questions against the governing drawing and standard.
Frequently asked questions
Why is true position twice the center offset?
The center offset is radial distance from the basic location, while a circular position zone is specified by diameter. Doubling the radial error expresses the result in the same diametrical convention as the callout.
Can different holes have different bonus tolerance?
Yes. Each row uses its own actual size, so features at MMC receive no size-derived bonus while features farther from the controlling material boundary may receive more.
Does the pattern pass if every row says PASS?
Only within this worksheet’s stated scope. The result does not prove conformance where datum mobility, simultaneous requirements, composite controls, pattern fitting, orientation, projected zones, or measurement uncertainty affect acceptance.
Can I paste directly from a spreadsheet?
Yes. Copy six adjacent columns in the documented order. The worksheet accepts the tab-separated cells produced by common spreadsheets as well as comma-separated CSV, including quoted CSV fields.
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