So, the RRampmeter is really the tool to use, since it can read direct from the track, and when you are not using it to chase down track issues, you can leave it in series with your output and measure DCC voltage and current… but if you don’t want to pony that up, any old DC meter with a full wave bridge converting the DCC to DC will be enough.
https://www.dccspecialties.com/products/rrampmeter.htm
In any case, this will help you stop burning out your bulbs… I first noticed this as I used to leave track power on all the time, with a couple of trains on the track, then I noticed one marker light was out, then another, and by the time I smartened up, I’d burned out the marker lights on a caboose and several locomotives… and as you know, Aristo steam loco marker lights are not sitting for sale on shelves in the local Walmart.
Best, Greg