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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Luke Deng ( )
Organization:Aerospace Industry Development Corp.
Date posted: Thu Mar 29 3:26:28 US/Eastern 2001
Subject: Maintenability Index
What's MAINTENABILITY INDEX meanning in physic and mathematic aspect?


Subject: Maintainability Index
Reply Posted by: Ned H. Criscimagna ( )
Organization: Reliability Analysis Center
Date Posted: Thu Mar 29 14:21:09 US/Eastern 2001
The maintainability index is a term used in two different ways. 1. It is used as a measure of the maintainability of software. > Maintainability Index - a measure of success - Set of polynomial metrics developed at the University of Idaho - Uses Halstead’s effort/module and McCabe’s cyclomatic complexity/module, plus other factors - Validated in the field by HP - Language independent - Index is a number between 0 and 100 - Used primarily to determine if modules have a high, medium, or low degree of difficulty to maintain > HP concluded “modules with a MI less than 65 are considered difficult to maintain” For more information on MI used in this way, go to or 2. It is also used as a measure of the total maintenance effort required to maintain a product in operational status per unit operating time. It is expressed as (from MIL-HDBK-472, dated 24 May, 1986): MI = (Summation (FRi) Mct Ti + Summation (FO) Mpt Tj)/T where: MI = maintenance index FRi = part failure rates (average part failure rates) Mct = mean corrective maintenance time Ti = operating time during calendar time Tj FO = frequency of occurrences of preventive maintenance tasks Mpt = mean preventive maintenance time Tj = calendar time in operating inventory T = total time

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