No, that was a spelling mistake. You surely didn't mean to say "Keeping people working sense (perception of external stimulus) 92." Instead, you meant to say "Keeping people working since (in regards to a past time) 92." It's not that "sense" isn't a word, it's that in your attempt to write the word "since", you misspelled it. I understand the argument that "although the word is used incorrectly, it is still spelled right and therefore a grammar mistake." but you must understand how idiotic that is. If you'd really like to get technical, it was a misspelling. A misspelling of a word, if you don't realize, is when you mean to spell out a word but the letters are skewed or out of place, sometimes even spelling a different word correct. Just because you happened to spell a different word, doesn't mean that your mistake was not a spelling error. I know it may be hard for you, since you (judging from our conversation so far) haven't graduated from elementary school yet. I hope I've helped you in not making yourself look like a fool in the future. TLDR; Just because you happened to spell a different word, doesn't mean that your mistake was not a spelling error.