Basically, with the rise of the Internet and more legitimate freelancing opportunities, one often has to gauge their time and whether or not that time is being monetized correctly. However, I do not believe in gauging everything by an hourly rate of pay.
Wage-rates are the domain of traditional work, and when you set at home most of the day, drinking coffee and writing $4 articles about the function of a urethra (for medical websites!), punching in and out of a time clock is an inadequate metaphor. You're a freelancer, after all -- technically every hour can be "on the clock." Plus, not all tasks pay the same. I have written a $15 article in five minutes, once, and a more complex $5 anatomy article in 45 minutes.
So, converting to a variable hourly rate, just for gauging one's level of productivity, is not really helpful. So, I have chosen to look at the day as a whole. How much did I make today? Versus How much did I make yesterday?
Thankfully, those daily totals are starting to improve again --- after a really shitty past two months.