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How do I check that a drawing revision lists every change?

Larry Wu, CEO, Kyumi · Last updated October 20, 2026

Compare the new drawing with the last released one in two passes: an overlay to find every visual difference, then a side-by-side read of dimensions, tolerances and notes. Balloon each change on the new sheet, then check that the revision block has a line for every balloon and no line without one.

Why changes go missing

A revision is meant to say exactly what changed. The 1997 edition of ASME Y14.35, as summarized in a 2008 NDIA overview, identifies where a revision changed the drawing in one or more ways, including a revision symbol in the field of the drawing, a description in the revision history block, and the zone in the ZONE column. When a revision has several changes, each one may get a sequence number in parentheses before its description (NDIA, ASME Y14.35 overview). Later editions may differ in detail, so check the edition your customer's drawing requirements name.

In practice the revision block lists the changes the engineer meant to make. It misses the ones nobody meant to make: a dimension that vanished when a view was rebuilt, a note edited while fixing a typo, a tolerance that changed because the model did. The supplier then finds them, or doesn't.

Worked example: 100-0412 sensor bracket, Rev B to Rev C

The change request asks for two things: move the 4x Ø3.4 mounting holes 2 mm to clear a new connector, and tighten the slot width tolerance. The files:

/100-0412 Sensor bracket/
  /released/
    100-0412.SLDPRT
    100-0412.SLDDRW
    100-0412_RevB.pdf            what the supplier has today
  /wip/
    100-0412_RevC_check.pdf      exported from the release candidate
  /review/
    100-0412_B-to-C.Compare.BMP  saved overlay result
    100-0412_B-to-C_changes.txt  ballooned change list

Compare the PDFs, not just the native files, because the PDF is what most suppliers build from.

Step 1: Overlay. In SolidWorks, Tools > Compare > DrawCompare shows the two drawings superimposed with differences in color, and can save the result as a .Compare.BMP file. It compares bitmaps, so it catches visual changes, such as an annotation moved 2 mm, but a changed custom property, such as the Description, is not reflected (SOLIDWORKS Help, DrawCompare). For PDFs from any CAD system, Acrobat Pro's Compare Files has a setting for scanned documents and drawings that compares pixels, and a side-by-side view that highlights each change (Adobe).

Step 2: Side-by-side read. The overlay tells you where something changed, not whether the new value is right. Open Rev B and Rev C next to each other and read every flagged zone: dimension values, tolerances, feature control frames, notes, material, finish and the title block. Then read the general notes and the default tolerance block even if nothing was flagged.

Step 3: Check what the sheet cannot show. Tools > Compare > Compare Documents compares the properties of two SolidWorks documents, and Compare Geometry shows faces and volumes that changed between two versions of a part (SOLIDWORKS Help, Compare Utility). This catches a model change that no dimension on the drawing calls out.

Step 4: Balloon and list every change. For 100-0412 the overlay found four differences:

# Zone Change found In the change request? Action
1 B3 4x Ø3.4 holes moved 2.0 mm toward datum A Yes Revision symbol, rev block line
2 C2 Slot width ±0.10 to ±0.05 Yes Revision symbol, rev block line
3 D1 Note 4 finish changed from bead blast to clear anodize No Confirm with the engineer; add a line or revert
4 B2 Reference dimension 12.0 deleted when a view was rebuilt No Restore it on the drawing

Place a revision symbol next to each change that stays. In SolidWorks, revision symbols are linked to the REV column of the revision table, and the ZONE cell updates when symbols are added or moved; the DESCRIPTION column is typed by hand (GoEngineer).

Step 5: Reconcile the revision block. Rev C now needs three lines, numbered (1) to (3), each with its zone. Check both directions: every revision symbol has a line, and every line has a symbol. Y14.35 says all changes incorporated at one time get the same revision letter, when the letter is assigned as the changes are incorporated (NDIA). Our advice: a change confirmed during this check goes into Rev C before it is released, not into a later edit of a drawing the supplier already has. (Three lines assumes the finish change in row 3 is confirmed, not reverted.)

Step 6: Keep the evidence. Save the overlay and the change list in the review folder with the release. When a supplier asks what changed, send the list along with the drawing, as in How do I make sure my supplier builds the right revision?

Ways to compare two drawing revisions

Method Good for Main risk
Printouts on a light table A quick look at a one-sheet drawing Misses small text and tolerance changes
DrawCompare in SolidWorks Color overlay of two native drawings Bitmap only, so property changes don't show; in our experience a moved view lights up everything
PDF compare in pixel mode Exported PDFs from any CAD system, with a side-by-side report Scale or sheet changes create noise that hides real changes
Side-by-side read Checking that values and notes are right Slow, and attention fades on long drawings
Model compare (Compare Geometry) Model changes the drawing doesn't dimension Needs both model versions; ignores annotations
Ballooned change list reconciled with the revision block Showing nothing was missed Only as good as the overlay that feeds it

When this stops working

  • Suppliers or inspectors find changes your revision block doesn't list.
  • Checking a revision takes longer than making it.
  • Several engineers change the same drawing in one revision, so no one person knows the whole list.
  • You can't say which overlay and change list belong to which release.

At that point the check needs to live with the revision itself, not in a folder beside it. Writing down why each change was made helps too; see How do I document why a part was designed a certain way?

FAQ

Can SolidWorks compare two drawing revisions?

Yes. Tools > Compare > DrawCompare superimposes two drawings and shows the differences in color. It compares bitmaps, so it shows visual changes, but a changed custom property such as the Description is not reflected.

What is a revision symbol on a drawing?

It is a symbol containing the revision letter, placed in the field of the drawing at the change. It is one of the ways ASME Y14.35 allows a revision's location to be shown, along with the description and zone in the revision history block.

Should the revision block list every change?

Yes. Y14.35 says any change to a drawing after release shall be recorded in the revision history block, and when one revision has several changes, each can get a sequence number before its description. A change that is on the sheet but not in the block is a change the supplier may not notice.

Which revision letters are skipped on drawings?

The 1997 edition of ASME Y14.35 uses upper-case letters in sequence and omits I, O, Q, S, X and Z. After Y, the sequence continues with AA, AB and so on.

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