My wife recently bought a selfie stick at Target for $5. It worked the first couple times she tried it after bringing it home from the store. However, problems emerged a few weeks later when she tried to use it again. We'd already thrown away the receipt, so fixing it was the only option.
My electric blanket has a "feature" that I really hate. It turns off automatically after "8 hours". I put "8 hours" in quotation marks, because I don't believe that's true. It seems like it often turns off much earlier than that. I can't say for sure because I've never measured it. Either way, it's an annoying feature. I like to sleep for 8 to 9 hours, I like to turn my blanket on 15 minutes before going to bed so it's warm when I get in, and I like my blanket to stay on for a little while in the morning so I'm not freezing when I wake up.
This post explains the math behind a very specific situation: charging a capacitor from 0 V to a fixed voltage through a resistor of known value. The time at which the capacitor begins charging is recent but unknown. By taking two voltage measurements a known amount of time apart while the capacitor is still charging, you can calculate the value of the capacitor.