pulseIn() function problem for measure frequency

I want to print out the period of the signal .

which is equal to 1/50.6=0.197

I want to know that is the value of duration equal to the length of the rise time ?

which is equal to half of the period 0.197/2.

Now the displayer just shown as 8117

Is there anything i can convert the value from 8117 to the period