I accept that that line is incorrect and i've taken it off. Thanks Steve. And sorry for the absence of comments in the code.
From 'z =(scale.get_units(), 3)' the purpose of z in the code is to collect the value that (scale.get_units(), 3) generates so I can use it in the control loop, because when I put (scale.get_units(), 3) in the control loop it doesn't work.
But even z does not assume the value that (scale.get_units(), 3) generates.
Apart from the fact that my control loop may have some problems, I think the main issue is that z cannot attain the value generated by (scale.get_units(), 3). Because if z doesn't hold the correct value, the control loop will not work correctly.
Maybe I'm not doing it the right way, I'm trying to make z assume the value of (scale.get_units(), 3) but I may be doing it the wrong way. Any ideas or alternatives please?