User talk:165.225.76.171

A = MUT/(MUT+MDT)= MTTF/MTBF=MTTF/(MTTF+MTTR)
there is a mistake in the calculation of availability : it's the ratio of Mean Up Time on the sum of Mean Up Time and Mean down Time. and le MUT is equal to the MTTF not the MTBF, then the MDT can be reduce to the MTTR if not considering the MRTT.

Look throught standards : EN 61703 (2017) or EN 50126-1 (2017). The confusion is common because MDT is negligible (one hour order) regarding common value of MUT (thousand or million order) to determine the reliability value, but the MDT can't be negligible to reliability value then use to calcultate the availability value.

Ps : MTBF = MTTF +MTTR is true only if failure rate and restore rate are constant in time.