OK, Cool  got it working (I was using those numbers in the corner at first, but thought I may have got it wrong when nothing happened so started toying with other numbers)
 turns out I had to restart again to get it to add the formula field, and then restart after entering the formula to get it to start implementing the formula.... AAAND my HEM was not configured right added to the difficulty discovering the issue...
Now, Next on the list (I see some quite usefull potential for this nifty plugin)...
I have a clamp on my house usage, and 1x clamp on each of 2x solar arrays, so have set up 2x virtual devices, one to show me net export/import, and one to show me the total solar production..... just need to get my formula right, and given I have no idea when it comes to luup, I need to know the correct syntax to bracketise the formula to make sure I get correct calculations?
ie can
power(30) >= 180 ? power(30) : 0
+
power(31) >= 180 ? power(31) : 0
be written something like.... (power(30) >= 180 ? power(30) : 0) + (power(31) >= 180 ? power(31) : 0) to show me total solar output while negating low readings on the clamps
and
Power(29)

power(30) >= 180 ? power(30) : 0
+
power(31) >= 180 ? power(31) : 0
as...... power(29)  (power(30) >= 180 ? power(30) : 0)  (power(31) >= 180 ? power(31) : 0) to show me net import or feed in (while negating erronius low readings from the inverters)??
I have it input with brackets as above, and it looks as though its working as it should, but, I couldnt say for sure  but I presume theres a definite right and wrong way so as not to end up with innacurate calculations in the event of more complex formulae??
Assuming all is right with that part (and we all know the result of assumptions!
)
taking it a step beyond....... I imagine from here I can activate a third "device" to on/off status as to weather I am importing (if the sum is positive) or exporting (if the sum is negative), which I can then use as part of a sceen to automatically power off unneeded devices if I am importing power? would be cool if I could find a way to triger a red or green image to display on the actual device performing the calculation for at a glance feedback (if its positive or negative) and set another variable on that device itself to 1 or zero accordingly to call upon or trigger other switches/sceens later??
Possible, or no?