The scale is the whole problem

Every argument about a takeoff eventually comes back to the same question, and it is never "did you measure that wall correctly". It is "what scale were you working at".

The number that multiplies everything

A takeoff is one calibration and then a lot of arithmetic. Get the wall lengths slightly wrong and you are slightly wrong. Get the scale wrong and every quantity on the sheet is wrong by exactly the same factor.

That is a nastier failure than it sounds, because a scale error does not look like an error. Wrong by a factor of two, the flooring number is still a plausible number of square feet for a room. Nothing about it announces itself. You find out when the material arrives.

Why the printed scale is not the answer

The obvious fix is to read the scale off the sheet. It says 1/4 inch = 1 foot right there in the title block.

Except that note is text, and text survives things geometry does not. Print the sheet to a different paper size and the note still says 1/4 inch = 1 foot while the geometry no longer does. Scale bars have the same problem in the other direction: they are drawn objects, and a scale bar copied from another sheet is a scale bar that is wrong.

The boring reliable answer

Click a dimension the designer wrote, and type what it says. It takes thirty seconds and it is the only statement of scale on the sheet that came from the person who drew it and that scales with the geometry when the page is resized.

Then look at what comes back. If the sheet says one scale and the calibration reports another, something is wrong and you know before you have measured anything. That is the entire value of showing the derived scale rather than hiding it.

Two habits worth having

Calibrate on the longest dimension. The click error is a fixed number of points, so it matters less the longer the line. A 20-foot dimension gives an order of magnitude better accuracy than a 3-foot one, for the same effort.

Recalibrate on every sheet. A site plan and a wall section live in the same PDF at scales forty times apart. Carrying a calibration between them is the most expensive mistake available.