Why calibrate
Scale presets work fine when you trust the drawing came out at a standard ratio. But:
- PDFs often get re-scaled or re-printed at non-standard ratios.
- Drawings exported by clients can be at unusual scales.
- A drawing may have a scale bar but no labelled ratio.
Calibration sidesteps the guesswork. You pick a feature on the drawing whose real-world length you know — a scale bar, a dimensioned wall, anything documented — type the expected distance, draw a line along it, and ZeroCount works out the scale factor.
When to calibrate
- The scale bar on the drawing is the only labelled measurement.
- The drawing's title block says
1:50but linear measurements come out clearly wrong. - You've manipulated the PDF (scaled, cropped, repaginated) and aren't sure what scale remains.
- High accuracy matters more than convenience.
For most off-the-shelf drawings at a standard scale, a preset is faster and good enough.
How to calibrate
- 1
Open the scale dropdown in the toolbar and choose Custom. The Custom Scale dialog opens.
- 2
Click the Draw & Calibrate tab.
- 3
In the Expected (m) field, type the real-world distance of the feature you're about to draw across. Placeholder:
e.g. 10. - 4
Click Draw & Calibrate. The dialog closes and the cursor enters draw mode.
- 5
On the drawing, click at one end of the known-length feature, then click at the other end. A calibration line is drawn between them.
- 6
ZeroCount calculates the scale factor automatically and applies it to the drawing. You'll see "Current calibration: [factor]x" the next time you open the dialog.
The Linear markers on the drawing immediately reflect the new scale. If you had existing Linear or Area markers, ZeroCount asks whether to recalculate them — say yes if the old scale was wrong.
Picking a good reference feature
Calibrate against:
- A scale bar with a labelled length. Pick the start of the
0and the end of the labelled distance. - A dimensioned wall — pick the two extremities that match the dimension.
- A standard module — for instance, the spacing of two columns on a structural grid, if it's documented.
Avoid:
- Features near the edge of the drawing — PDF rendering distortions are largest at the edges.
- Features at an angle — small click errors translate into larger scale errors. Pick something perpendicular to the screen.
- Drawings that have been rotated after the PDF was generated — re-rotation can introduce non-uniform scaling.
Calibrate against the longest known distance you can find. A 10 m calibration line gives you a much more accurate scale than a 1 m one — small click errors are diluted across the longer distance.
Manual Entry — the alternative
The same dialog has a Manual Entry tab. If you already know the scale ratio:
- 1
Click Manual Entry.
- 2
Type the second number of the ratio in the input field next to 1 :. For 1:100, type
100. Placeholder:e.g. 100. - 3
The display below shows "Scale: 1 : [value]" confirming what you've typed.
- 4
Click Apply Scale.
Use this when the scale is a known ratio that just isn't in the preset list.
Resetting calibration
If you calibrate, then realise you got the expected distance wrong, you can clear the calibration:
- 1
Open the Custom Scale dialog again.
- 2
Click Reset Calibration at the bottom. The button only appears when a calibration is active.
- 3
The calibration factor goes back to
1.0000xand the drawing reverts to using its preset scale.
You can then pick a preset, recalibrate, or set a Manual Entry value.
Per-drawing vs per-group calibration
A calibration applies to the whole drawing. It's saved on the file, so reopening the drawing keeps the calibration.
If you also have per-group scales on Linear or Area groups, both are applied — the calibration factor scales the drawing units, and the group scale converts them to real-world distance.