True Position

Definition

Geometric tolerance that controls feature location relative to datums.

Use the frontmatter definition as the controlled meaning for setup, machining, and inspection decisions.

Formula / Rule

• For a 2D hole-center check, a common calculation is TP = 2 × sqrt((ΔX)^2 + (ΔY)^2) in the drawing unit.
• Evaluate true position against the active datum structure, not against free-state coordinates.

Typical Range

• Review the tolerance as a diametrical zone and confirm whether MMC/LMC modifiers change the effective limit.
• Check X/Y drift together; a single-axis result can look acceptable while combined position does not.

Shop-floor Scenarios

• Use true position to review hole patterns before committing rework on a precision plate.
• Compare measured center drift with the active datum before moving offsets on a multi-feature part.

Common Errors / Troubleshooting

• If holes fail true position unexpectedly, verify both datum lock and hole-center measurement method before reworking parts.
• If correction makes one feature better but another worse, check whether the active datum or pattern origin is wrong.

Related Tools

• True Position Calculator
• Gdt Reference