How to correctly take into account the timing of the developer?

Question

Work organization

The question is quite general.
Programmers who work by the hour, how exactly do they account for how much time they spend on something. After all, debugging and testing takes a lot of time.
Another question is how the client can understand whether the developer has been working on his project for the specified number of hours or the programmer has overestimated the cost of his work. Are there any online services for recording the time spent on development so that the client pays "according to the meter" (time tracking)

Answer 1

There are developers who work fast, but expensive. There are those who are long and cheap. Other combinations are also possible.

The developer works on the result, not on time.
Indirectly, the work of a developer can be measured by the number and volume of commits. But just like time, so-so indicator. Depends on the complexity of the task or specific solution. Well, you can commit a lot of garbage code that will not carry a payload, but will create the appearance of work.
Evaluation can only be based on personal preferences and feelings. If one of the developers is closer to the center of the diagram, cooperate with that (if we talk about freelancers). Businesses rarely attempt to use a "counter" at all, except perhaps in some state bureau originally from the USSR