I have no room for a regular 'step' scale to weigh the tank. So, I thought tying a small rope to the neck of the tank (so as not to interfere with the valves), and using a digital fishing weigh scale to check the tank. Hook the scale to the rope and lift.
My tank sits behind the tank, and off to a side - which makes it very hard to reach.
Hope this helps some others. I won't trust a small pressure drop on the main pressure gage. Weighing it gives a much better idea of the amount of CO2 left.