Cooking can be tricky — what exactly qualifies as “diced?” What’s the difference between a simmer and a boil, anyway? But at least one thing seems easy: preheating the oven. If the recipe says set oven at 375 degrees, all you have to do is set the oven to 375 degrees, right?Wrong. We have been lied to: Oven temperatures can actually range regularly below or above the set temperature. So, how can you tell what your true oven temperature is? One easy way involves baking a tube of Pillsbury biscuits. The recipe is so foolproof, that if you follow the baking instructions perfectly, your biscuits should also turn out perfectly — that is, if your oven isn’t lying to you.Simply spread out the biscuits evenly on a cookie sheet and cook in the oven for the exact time specified on the tube (no peeking; opening the door will lower the internal temp and tamper with your results). Once the time is up, take the biscuits out and see if they’re underdone, overdone, or just right. This tells you if your oven runs cool (underdone), hot (overdone), or actually at the correct temperature (perfect). Depending on what you find, you may want to extend (or shorten) baking times, or consider adjusting the display temperature a little to try to get closer to the actual desired heat.Of course, you could buy an internal thermometer for your oven to find out the same info, but this hack has a clear advantage: Once you've done the biscuit test, you're halfway to a homemade brunch. ( Lifehacker