Assuming you have only ONE X-axis scale and ONE Y-axis scale, it's easy:
Use a property node for the graph, and choose the XSCALE : MAPPING MODE and YSCALE : MAPPING MODE properties: Set them to 0 for linear or 1 for logarithmic, based on some switch on the front panel.
If you have more than one scale, you'll have to set the ACTIVE SCALE to 0, set MAPPING MODE to whatever you like, set ACTIVE SCALE to 1, set MAPPING MODE to whatever you like, etc., etc.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
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Blog for (mostly LabVIEW) programmers: Tips And Tricks