Without selecting any layers, the specs will display the distance between them as you move between the layers.
Select a layer and mouse over another layer to display the specs for the distance between the two layers.
Multiple Layers Markup
Hold down the Ctrl key and select multiple layers to display the distance between multiple layers.
iDoc supports to view specs in percentage by pressing Alt.
Set as Reference Layer for Percentage Specs
Right-click on a layer to set it as the reference layer for percentage specs. This layer will be used as a reference to calculate the percentage value of the specs. (Press Alt for percentage specs)