Being in a business where you’re charging your clients for the amounts they’ve used (hours fee etc.) and adding also a fixed charge, i.e. use of an item during this time and so on, means you’re essentially charging your customers for two separate things. 

In doing so one thing you must always remember is that showing those two or more services on the invoice needs some consideration. It’s not just adding everything up and naming the line on the invoice something fancy like “use of this and that” or something similar, but making the invoice as useful to the receiving party as possible. Namely what’s expected is that you split up as much as possible by also showing the prices separate for each component. One might ask “why?”

The reason why you’d do it is obvious if you think of situations where the expense is split between people for an example and only one of them choose to use this specific item we mentioned. It’s those little everyday situations even you may have come across and just for them, for making your customers’ lives a lot easier or simply making a gesture. Think about it for a second if you were the client and got the invoice you’re giving out now.