When I got my PCB back for my Connect4 I soldered all the components
onto it but I left one of the LED's loose, reason being that I wanted to
use an ammeter on it to see exactly what current I had flowing through
the LED's.

There was a resistor in series with the particular LED whose current I
wanted to know; I could have soldered the LED permanently in place and
then used a volt meter across the resistor and from there used Ohm's Law
to calculate the current.

I'm just wondering though what would be the "professional" way of doing
this? Would you leave the LED loose and use an ammeter, or would you
solder it in and use a volt meter?

I wonder would you get better accuracy with an ammeter? The volt meter
will draw a tiny bit of current which will affect the circuit... but
then again the ammeter won't have zero resistance so that too would
affect circuit.

Or is the difference so negligible that it's not even worth debating... ?

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