Testing

 Been testing things by running the same code on two different

computers: an older one, with 2 cores; and a recent one with 4.

Apart from minor speed differences, both behave the same way

with my python code. 

In principle, a quad core processor is capable of parallel computing,

while a dual core processor isn't; but it didn't seem to make a difference

in what is possible. Not for this scale of effort, in any event.

                                                       

In effect, both complained if I tried to run a mix of a function call and two threads.

Error: main isn't running in mainloop ie I am trying to change the look of things

from threads, and this is not recommended.

Did use both time.perf_counter and time.process_time to track how lomg.

The first takes sleep time into account, the second one doesn't. Intriguingly,

my newer computer reportedit took 0.0 seconds to run the above code with

processing time. (Both need to be used as finish - start!).