Capture a known distance between two objects and then calibrate or adjust your sheet to reflect these dimensions and measurement units.
You must specify the scale on a sheet before you can perform takeoff on it.
Click Scale not set at the top of the sheet in the viewer. Alternatively, select Calibrate
from the viewer toolbar.
Select two points on the sheet.
In the Calibration dialog that opens, define the size and unit type of the dimension you just drew, then click Set calibration.
The scale for the sheet is now set and will be set for anyone viewing this sheet in the project in Takeoff.