Viewport Scale Drift on a Multi-Sheet Layout
A drafter has one layout tab containing four viewports for a building's four elevations, each intended at 1:100 on an A1 sheet (841 x 594 mm). She sets each viewport's standard scale to 1:100 using the viewport scale list. Later she resizes the sheet by editing the page setup to A2 (594 x 420 mm) and pans one viewport to recenter the north elevation. At plot time, the north elevation measures differently from the other three when checked with a scale rule, and its annotation text looks larger relative to the drawing than the others. The other three viewports still check correctly. She did not lock any viewports.
1. Identify the most likely cause of the north elevation's scale error and explain the mechanism.
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The north viewport was almost certainly changed from a standard scale to a custom scale when it was panned. Panning alone does not change scale, but if the drafter used a zoom command inside the viewport (for example ZOOM with a factor, or scroll-wheel zoom) rather than PAN, the viewport scale becomes a custom ratio and the scale list shows a non-standard value. Resizing the sheet or the viewport frame does not change the model-to-paper ratio for a locked standard scale, but an unlocked viewport can drift with any zoom operation.
The clue is the annotation size: annotation scaling is tied to the viewport's scale, so text at an annotative size appears larger if the viewport scale became larger than 1:100. The other three viewports were untouched and remain at 1:100, which is why only the north elevation fails the scale-rule check.
2. Describe the corrective procedure and the preventive setting the drafter should adopt for all viewports.
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Corrective steps: enter the north viewport, open the viewport scale list, and reselect 1:100 so the custom scale is replaced by the standard one. Then use PAN (not zoom) to recenter, confirm the scale still reads 1:100, and verify with a known dimension or a scale rule. Check that annotative text displays at the intended size and run REGENALL if needed.
Preventive setting: lock every viewport after its scale is set (Viewport Lock, or the lock icon in the status bar when the viewport is active). Locking prevents zoom and pan from altering the scale while still allowing panning within the locked viewport. She should also confirm the page setup size is final before distributing viewports, and use PAN rather than wheel-zoom inside viewports as a habit.