Changing symbology orientation in QGIS

Question

I have a project based on data from a water company, but the arrow heads are all pointing in the wrong direction to indicate the direction of flow. Basically I need to turn all the SYMBOLROTA values to negatives. How can I change all the values of a set of features to become minus - it might be a search function of a script or something?

Better than that would be to be able to change the type of rotation (like you can do in AutoCAD) to be anti-clockwise rather than clockwise. I haven't been able to find out how to do that but that would be the easiest?

Answer 1

We worked it out - in the attributes table there's a Field Calculator where you can do various calculations based on the data. We selected all the data points and then opened the Field Calculator and updated the existing field (tickbox near top right) and applied the simple calc "SYMBOLROTA" * -1 which just multiplies all the values in the SYMBOLROTA column and puts the answers back in the SYMBOLROTA column replacing the original values.