I have a contract to upgrade some in-house software for a large company. The company has requested multiple feature additions and a few bug fixes. This is my first freelance style job.

First, I needed to become familiar with how the application worked - I learnt it as if I was a user.

Next, I had to learn how the software worked. I started with broad concepts, and then narrowed down into necessary detail before working on each bug fix and feature.

At least at the start of the project, it took me a lot longer to learn the existing code than it did to write the additional features.

How can I describe the process of learning the existing code on the invoice? (This part of the company usually does things in-house, so doesn't have much experience dealing with software contractors like me, and I fear they may not understand the overhead of learning someone else's code). I don't want to just tack the learning time onto the actual feature upgrade, because in some cases this would make a 'simple task' look like it took me way too long. I want break the invoice into relevant steps, and communicate that I'm charging for the large overhead of learning someone else's code before being able to add my own to it.

Is there a standard way of describing this sort of activity when billing for a job?