I want to convert the type of some fields in a vector layer from String to Real. I am trying to use the Processing -> QGIS geoalgorithms -> Vector table tools -> Refactor fields tool to do this. When I open this up and select the layer I'm trying to edit, a dialog pops up that asks "Do you want to reset the field mapping?" (Yes/No) ... I can't find documentation anywhere on what this means.
Can someone explain?
(See lower center in image for dialog I'm referring to)