A practical reading order
Read the drawing notes; locate the controlled feature; identify the control and tolerance-zone shape/size; read modifiers in their actual positions; establish required datum references; check the related size limits.
No datum is not automatically an error
Some controls are independent of datum references. Form and profile cannot be reduced to the old rule that every feature control frame needs a datum.
Do not mix default rules
ASME Y14.5 and ISO GPS do not share all size/form defaults and interpretations. Do not assume a diameter alone permits arbitrary form or that one system can silently substitute for the other.
Continue your task
Sources and review scope
Reviewed 23 October 2026. Arithmetic examples are labelled separately from source-table facts and standard scope.
ASME Y14.5-2018 (R2024)
Public standard catalogue and scope. Full clauses are not reproduced or independently audited here.
Open the original source ↗ISO 1101:2017
Public scope for geometrical-specification symbols and interpretation. Do not substitute it for ASME drawing rules.
Open the original source ↗KEYENCE — GD&T drawings and symbols
Manufacturer teaching: control groups, profile with/without datum relationships and theoretically exact dimensions. Not an exhaustive ASME 2018 symbol table.
Open the original source ↗