The term yield means to bring forth and is defined as output over input.
Yield = Output /Input
If 100 units are input into a system and during processing 10 units become defective, only 90 good units will be produced as output. The resulting yield would be 90/100 = 0.90 = 90%. If each unit input into the system was valued at $10.00, a total value of $1,000 was input into the system. At 90% yield, the value of output is only $900, neglecting any value-added work done by the system
Even if the yield rate is greater than 99% in eachstep, due to the number of steps the final yield can drop to 75%