I generally do not check on them at all. Let them be until finished. Lenght of that depends on style, wheat beers 2 weeks, most others 3-4 weeks. I have my process down well enough that I do not bother with unrequired gravity readings. Just do one at the end when I bottle/keg. Honestly that's not really required at all either. Once you have been brewing a while, you realize that the yeast know that to do without much help from you. They are also very good at what they do.
A 2006 study found that the average American walks about 900 miles a year.
Another recent study found that Americans drink an average of 22 gallons of beer a year.
That means, on average, Americans get about 41 miles per gallon.