GeekDad Puzzle of the Week – Flipping Digits

Last night, at an auction for the kids’ school, we got an interesting auction ID number, as shown below.

It was one of the few bidding numbers we saw with a hand-written “bottom bar” below the number. Our friend, Tom, with #12, also had a hand-written bar applied. Thinking about it, I can see why they applied the bar — in the heat of bidding, if I held my number less than upright, I could inadvertently apply a bid auction participant #89.

This week’s GeekDad Puzzle of the Week is simple: If there were 650 different participating parties in the auction, each with their own consecutively determined number, how many numbers required a bottom bar to avoid possible bidding confusion?

As always, please send your best guess or definitive answer to GeekDad Central. If your submission is correct, or at least reasonably close, it will be entered into a random drawing for a chance at a $50 Gift Certificate from the fine folks at ThinkGeek.

Good luck, and happy puzzling!