When placing in-span equipment, the 'From structure' selection will change where the equipment is positioned, as the position of in-span equipment is measured in the direction of increasing chainage from the selected structure.
In the example below ‘DD-10-31’ is the selected structure, which is in the bottom left. The value in the 'Distance' section, whether 'Ratio' or 'Absolute', defines the distance from that structure in the direction of increasing chainage that your in-span equipment will be placed.
If you were to select the next structure along as your 'From structure', it would position your equipment in the following span.
Next steps: Learn how to place in-span equipment here.