Geometric Dimensioning and Tolerancing (GD&T) is the language that links design, production and metrology. Applied well, it helps ensure a part assembles and functions as intended; misinterpreted, it produces conflicting measurements, scrap and costly back-and-forth 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.
In a guidance article, the company sets out four practices intended to make GD&T handling more reliable, from reading design intent through to the reports handed to the shop floor. The recommendations describe how its Metrolog software implements each step; the benefits cited are the vendor's stated expectations rather than independently verified results.
1. Start from the PMI
Using PMI requires decoding design intent: which feature is targeted, which references apply and which tolerance is specified. Metrologic DCS argues this step is error-prone when performed manually, because a value copied incorrectly or a reference misunderstood means the part is inspected against a requirement that was never specified. The suggested approach is software that takes the PMI as its starting point rather than asking the user to re-enter tolerances, so that features and their evaluations are created from the part's digital definition. The stated result is no re-keying, fewer interpretation gaps and time saved from the very first step of program preparation.
2. Do not rebuild the DRF by hand
The Datum Reference Frame (DRF) defines where measurement starts. It is built from reference features (A, B, C) and determines which of the part's degrees of freedom are constrained for the evaluation. If the frame is constructed in the wrong order, or the degrees of freedom are poorly selected, the same part can be declared conforming or non-conforming depending on the operator, which the company identifies as a major source of GD&T misinterpretation. Automating the step so that the DRF and its degrees of freedom follow the drawing definition rather than operator choice is presented as the way to make results repeatable from one operator, one machine and one site to the next. In Metrolog, the DRF is created automatically when a GD&T is evaluated, and the degrees of freedom are selected accordingly.
3. Reuse imported DRFs to limit rework
References A, B and C already carry labels placed by the design office in the CAD model. Recreating them during program preparation wastes time, opens the door to discrepancies and forces rework whenever a definition changes; on a part with many annotations it is also difficult to track which ones have been handled and which remain to be measured. The recommendation is to start from the DRFs coming from the PMI and predefine GD&T from them, while keeping a clear view of where each annotation sits on the part and where its measurement stands. Metrolog's Scan GDT function reads the decoded PMI and assigns a status so that both the decoding and the measurement can be validated.
4. Tailor reports to the reader
A report limited to pass or fail does not tell the shop floor what to do, the company argues: an operator who does not know which defect they are dealing with adjusts by trial and error, which produces scrap and correction loops. The suggested split is a table of numerical values for quality control, a Go/No-Go report for a quick decision and a decomposition analysis for the operator. Metrolog separates the defect of an evaluated feature into four independent types, namely form, size, position and orientation, alongside the global defect, so that the dominant type, and therefore the first correction to make, is immediately visible. A good report, the company states, reduces scrap and speeds up corrective action.