If you have a predetermined linear length that you need to measure (EG 3.6m lengths of busbar) you can use the "snap to" tool to measure quickly and accurately.
Click on the "Measure" tab at the top left of the page (Shortcut to cycle through tabs = W)
Create a linear measurement
Click on the advanced options (3 small dots to the right of the measurement's name)
Set the length in the "Snap to:" box
Create the length needed
How to: Measure lengths.