Degree of Financial Leverage?

First of all its very to important to understand how does Fixed cost mechanism work, irrespective of entity's sale the Fixed cost remains constant.

Interest expense on Amount borrowed is a type of fixed cost.

Now assume that an entity has
Debentures @ 7% - 1000
10 Equity shares - 1000 (If no Debentures then 20 Shares having value 2000)

E.g. Entity earns 500
EPS if Debentures - (500-70)/10 = 43
EPS if no Debentures - 500/20 = 25

Therefore when we use Financial Leverage the Investor earns a higher Earning. But this is only possible when the Return on Investment is greater than the borrowing rate.

Thanks for explaining the leverage effect on EPS but what is the formula for degree of financial leverage and what does it signify?