Scale

There are three scale factors: 1:1, 1:50, 1:100.
When measuring in Model space, the scale factor is 1:1 by default.
When measuring in paper space, if specified points by snap in the viewports, the scale factor is the same as the scale factor of the viewports, otherwise the scale factor is 1:1.

Set current:
Click one factor to set it to be current scale factor in the list.

Delete a scale factor:
Long pressing on a scale factor or sliding from right to left , it prompts to delete it.

Add a scale factor:
Users could add a new scale factor by clicking “Add” button on the top right corner and entering a new scale factor in the dialog box.
Users could also speicfy a scale factor by measure a distance. The new scale is the ratio of the measured length to the desired length, so users should enter the desired length after measuring length.