Geometric Dimensioning and Tolerancing (GD&T) is the language that links design, production and metrology, and when it is misread it produces conflicting measurements, scrap and repeated exchanges between teams. Metrologic DCS notes that with Product Manufacturing Information (PMI) increasingly embedded in CAD files and standards still evolving, the opportunities for error keep multiplying, and sets out four practices for a more reliable chain from design intent to shop-floor reporting.
Start from the PMI
Using PMI means decoding design intent: which feature is targeted, which references apply and which tolerance is specified. Metrologic DCS describes this manual step as error-prone, because a value copied incorrectly or a reference misunderstood sends a part to inspection against a requirement that was never specified. It recommends software that takes the PMI as its starting point rather than making users re-enter tolerances, so that features and their evaluations are generated from the part's digital definition — no re-keying, fewer interpretation gaps and time saved from the first step of program preparation.
Automate the datum reference frame
The Datum Reference Frame (DRF) establishes where measurement begins. Built from reference features A, B and C, it fixes which of the part's degrees of freedom are constrained for the evaluation. If it is constructed in the wrong order, or if the degrees of freedom are poorly selected, the same part can be declared conforming or non-conforming depending on the operator, which the company calls a major source of GD&T misinterpretation. Automating the step ties the DRF and its degrees of freedom to the drawing definition instead of operator choice, making results repeatable across operators, machines and sites. In the company's Metrolog software, the DRF is created automatically when a GD&T is evaluated.
Reuse imported references, and report for the reader
Because references A, B and C already carry labels placed by the design office in the CAD model, recreating them wastes time and invites discrepancies, particularly on heavily annotated parts where it is hard to see which callouts remain to be measured. The company advises starting from PMI-derived DRFs and using Metrolog's Scan GDT, which reads the decoded PMI and assigns a status so that both decoding and measurement can be validated. On reporting, it argues that a pass-or-fail verdict gives the shop floor nothing to act on: numerical tables suit quality control, Go/No-Go suits a quick decision and decomposition analysis suits the operator. Metrolog splits the defect of an evaluated feature into form, size, position and orientation alongside the global defect, so the dominant type is visible first.