Usually making print screen is enough, and making photo of your display is definitely an overkill :)

So, If you want to have at least 50 empty barrels at each station you don't need counter at all.
Const combinator: "-15 empty barrel"
Fast inserter: "empty barrels < 0"
https://fat.gfycat.com ...

You can use rail signal right ahead the train stop to detect when train leaves from the station and reset your counter.
Also, some pictures/blueprint of your setup could be useful to give more detailed help.

I can take a picture of the counter I have but other than that I don't have anything at ...

Hey everyone!

I read through the Combinator help page before posting this, I've watched several youtube videos and searched for a design. I've fiddled for a couple days trying to get it to work properly and can't get this last part down.

I am using barrels on trains for oil. I want to have a ...