If you are trying to discover how far along a person is with a particular project or job, instead of asking "what percentage complete are you?" (or "how far along are you?") ask the following:
How long have you spent on the project?
How much longer do you need?
By asking percentages, you are likely to get answers like 50% or 80% or 30%, which often have no relationship to where the project really is.
By asking times, while it is still a swag, it is a more realistic swag.
When someone says "two hours", resist the temptation to say "what did you do the other 6 hours?" or you are likely to get told "eight hours" next time! Instead, go to the second question. Track how long tasks take and you'll do a better job as you go on estimating who can get things done right and how long it will take.
I always think I can do projects much faster than those who work for me or in the group I am in. As an entrepreneur I often have to remember that no one is going to do the job the way I will do it. But I can be more systematic about assigning work and time it takes to get the job done right.