I was paying a fine at the library recently and I watched in horror as the girl collecting it struggled with basic subtraction. She was just not able to make the right change. I was close to letting her keep the 30 cents she owed me if that put her out of her misery. I had to wonder how such a severe arithmetic impairment impacted the rest of her life. At twenty something it is probably too late to mend the problem.
When people start to need devices like Drop to adjust their recipe for the ingredient they are short on, you know commonsense has left the building a while back. It would be a lot more useful to make mental math mandatory in school and get rid of calculators until the end of high school. The fine folks that came up with the idea of Drop could put their skills to better use and create something that served a real need. Making people more arithmetic challenged than they already are is not the best line of work to be in.