HOW WAS PROFIT MADE IN THE STOCK MARKET CRASH OF 1929?

This is from the website about the batch marketplace pile-up of 1929:

“For each dollar invested, the domain user would steal 9 dollars value of stock. Because of this leverage, if the batch went up 1%, the financier would have 10%! ”

I do not assimilate how the 10% distinction was made.
How WAS the 10% distinction made?

Please help! Thanks!