Reg:MTBF Calculation

Hello Experts,

My client needs to have MTBF Formula which is to be customized .The formula used is MT BF = total no of machines(total available hours-total B/D Hours)/total number of B/D 's.

But in standard SAP there is ONLY MTBR Formula which is not same as MTBF. i WANT To know from where we take total B/D Hours for the formula from MCJB Report we are getting output for total b/d hours .but its difficult for me to find wher the data is getting stored to calculate for the formulae.

Can any body show more light or possible suggestions for calculating MTBF or can we derive the formulae from MTBR.

REGARDS,

SATISH.