Why scale is different from every other mistake
The software cannot determine the true scale of a PDF by itself. A drawing that has been printed to fit, exported at a different paper size, scanned, cropped or rescaled will look completely normal on screen — and will produce quantities that are wrong by a constant factor. Every number on the sheet is wrong in the same proportion, which is precisely the kind of error that survives a quick sanity check: the totals still add up, the ratios between items still look right, and nothing on the page looks broken.
How it happens
- Printed to fit. An A1 drawing exported to A3 keeps its title-block scale note (say 1:100) but is now physically half the size. Set 1:100 and every length is halved, every area quartered.
- A nominal scale that is not the drawn scale. Title blocks are copied between sheets. The note says 1:50; the sheet was drawn at 1:100.
- Scanned or photographed. A scan is never exactly to scale, and a phone photograph is not to scale at all.
- Cropped or re-saved. A PDF passed through another program can be resampled without anyone intending it.
How to check, every time
- Calibrate from a dimension that is written on the drawing, never from the title block alone. Pick a long, clearly dimensioned line — a grid line, an overall wall length — and measure it. The software sets the scale from what you measured against what the drawing says it is.
- Verify with a second dimension in the other direction. A drawing that was stretched to fit a page is out of scale by a different factor horizontally and vertically. If the second check does not agree, the sheet has been distorted and no single scale is correct.
- Sanity-check one quantity against something you know. A door opening is about 0.9 m wide; a standard block is 440 mm long. If a measured door reads 1.8 m, the scale is wrong by two.
- Re-check after replacing a drawing. A revised PDF is a new file, and its scale is not the old one’s until you have measured it.
What the software does, and does not do
CostTakeoff records the scale you set, shows it on the drawing, and marks a drawing whose scale has not been verified. It performs the arithmetic from that scale. It does not know the true size of anything on the sheet, and it cannot tell a correctly scaled drawing from one that has been printed to fit. Checking the scale is part of the measurement, and it is yours.
The Terms of Service say this in fewer words: what the Service is, and what it is not.