How do I know if an interview went well?

Hi there... it sounds like the interview went well, but remember.. there may be others interviewing as well... I would be cautiously optimistic. For a professional job like Product Development, I would go with a typed thank you letter - be sure to mention something that was "personal" to your interview - ie. I was really excited when you mentioned in the interview about new product x that is currently in development, and have many great ideas that I would love to share with the team" - something like that. Also send a separate, unique letter to each member of the interview team. Also call at week's end if you haven't heard, just to check in.. just don't call 10X or you will annoy them :) Good luck to you!!