A coordinate is a location relative to an origin. Changing that origin can change every displayed value without moving the part.
Locate the coordinate origin
Ordinate dimensions report horizontal or vertical feature distances from a defined origin. Their values belong to that coordinate reference. Different views or drawing records can use different origins, so equal-looking coordinate fields are not automatically comparable. Primary reference: Autodesk: ordinate distances from a defined datum origin.
Retain the origin point and positive directions with the feature identity. A datum used as a coordinate origin in a software explanation should not be taken as certification of a complete physical datum-reference specification. The actual drawing must define its intended reference.
Translate an invented origin
Suppose a fictional feature lies at x = 35 mm relative to originA. OriginB is 10 mm farther along the same positive x direction. The feature's coordinate relative toB is 25 mm. Its physical nominal position has not changed; the reference location has.
The difference 35 minus 10 equals 25 only under the stated parallel-axis arrangement. A rotation of the coordinate directions would require another transformation. The scenario describes nominal coordinate interpretation, not a measured position or a permissible location error.
Compare references before comparing numbers
Identify each drawing's origin, directions and model orientation. Trace the same feature into a common definition before treating differing ordinate values as a design disagreement. Include enough surrounding geometry to locate the reference when sending a cropped hole-position record.
For a mating pattern, compare the complete required point relationship rather than only one isolated coordinate. Origin identity and feature identity must both survive the handoff. Once the nominal definition is consistent, the actual manufacturing and inspection requirements can be assessed against the correct location instead of an accidental difference between coordinate systems.
Customer Questions
Can coordinate values change without moving the part?
Yes. Changing the origin can change their values.
What is the fictional coordinate relative to originB?
25 mm under the stated parallel-axis translation.
Does the same subtraction handle a rotated system automatically?
No. Rotation needs its own coordinate transformation.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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