Basic formula in Post Process not working

It seems the basic formula in Post Process has problem. I tested following formulas and only 2nd one is working.

First, it takes a very long time to process a large data set, and there’s not necessarily any indication that the command has been accepted and processing has started.

Second, both formula: 2*f2 and formula: (2*f2) work for me, but formula: (f2*2.0) fails with the message:

STOPPING could not understand your formula SORRY....

as does formula: f2*2:

STOPPING could not understand your formula SORRY....

but with no further explanation - in the guide Emoncms Post Processor - Guide | OpenEnergyMonitor or on-screen. It also appears that the order in which you click “Auto refresh” and “Run process” has a bearing on what happens.

I’d suggest the documentation is not adequate. Are floating point values not permitted? - this is contrary to the on-screen example if so. There needs to be a definitive list of the types of values and the operations that are and are not permissible, and the order in which processing takes place. Why is the on-screen example (f12-f13)*(f7-f11) not permissible?

And what does

The also needs to be some clarification about when “Auto refresh” should be activated or deactivated, and indeed whether it relates to the display or the process.

I’m sorry I can’t take this task on - it would take me far too long as I have limited experience working in PHP.