Several labelled offsets can describe the same feature pattern. Read where each distance begins before adding the numbers.
Identify the start of each offset
Baseline dimensions describe several distances from a shared base point. Chain dimensions describe successive distances starting from the preceding point. Their extension-line references identify which nominal positions the values connect. Primary reference: Autodesk: baseline and chain dimension relationships.
Do not add all baseline values as though they were consecutive segments. Similarly, a chain value is not automatically the total distance from the first origin. This distinction concerns nominal geometry before any separate allowance or tolerance calculation is introduced.
Reconstruct an invented point pattern
Imagine three points lying along one axis at positions 0,20 and 50 mm. A baseline record from zero can report 20 and 50 mm. A consecutive chain can report 20 and 30 mm. Both records describe the same ideal positions.
Adding the baseline values would give 70 mm, which is not the final point's coordinate in this example. Adding the chain values gives 50 mm from the initial origin. These calculations are not a tolerance-stack analysis and establish no permitted accumulated error.
Read the nominal pattern consistently
Mark the actual dimension endpoints when translating a drawing into an interface table. Keep the shared origin for baseline records and the sequence of connected points for a chain. Where the pattern uses several directions, document each direction rather than summing unrelated distances.
Compare the resulting nominal locations with the mating definition. If two drawings use different dimension styles, reconstruct their points before declaring the values incompatible. The intended nominal relationship can be identical even when the printed numbers differ, while actual tolerances and inspection references still require their separate specified interpretation.
Customer Questions
Should all baseline values be summed?
No. They can share the same starting point.
What chain describes the fictional 0,20,50 mm positions?
Consecutive lengths 20 and 30 mm.
Does this nominal comparison calculate accumulated tolerance?
No. Tolerance evaluation is a separate defined problem.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
Discuss Your Machine Requirement
Share your product, container, required output and the evidence needed for your technical review.
Request a Technical Review