"7: Key numbers: Do not get long on a trade above the last two numbers above 85 through 15 or short with the last two below 15 through 85. The whole numbers often time create great resistance and the market typically reaches them and turns around a couple of time before actually breaking through the whole numbers. The closer that the last two numbers are to being 50 the better off you will be with your trade. "

I don't understand what the author means by key numbers?

Anybody want to elaborate on that?

thanks

Sada