A car with a heated windscreen is a boon!
I knew there would be a clever dick poster like you, but not such clever dick, what about the parts of your windows that are not heated, you're supposed to clear the lot before you drive away.
Whilst I'm sure none of us are that saintly and clear all of our window space before driving off but you would still be able to see that it's a scraper day even if you have a heated windscreen, so there, my scraper calibration idea would still stand.
You always get someone that tries to rubbish any perfectly sensible idea.
ippy