20.4 High Return on Investment

18.2 Personal Software Process ^SM

Let's use our total life cycle cost model to determine the cost of developing 10,000 lines of code using software testing. The formula is software size multiplied by 10.51, less the test hours times nine. Our total life cycle cost for using software testing alone is 45,100 hours.

Let's use our productivity model to determine the old productivity of using testing. The formula is software size divided by the total life cycle costs of testing. Divide 10,000 by 45,100, and the old productivity of testing is 0.22.

Let's determine the total life cycle cost of developing 10,000 lines of code using the Personal Software Process ^SM . The formula is software size divided by 25. Our total life cycle cost for using the Personal Software Process ^SM is 400 hours.

Let's use our productivity model to determine the new productivity of using the Personal Software Process ^SM . The formula is software size divided by the total life cycle costs of the Personal Software Process ^SM . Divide 10,000 by 400, and the new productivity of the Personal Software Process ^SM is 25.00.

Let's determine the difference between the old productivity of testing and the new productivity of the Personal Software Process ^SM . The formula is old productivity of software testing divided by new productivity of the Personal Software Process ^SM . Divide 0.22 by 25.00. The difference between the old productivity of testing and the new productivity of the Personal Software Process ^SM is 0.01.

The special, new, or additional costs that are required to introduce the Personal Software Process ^SM consist of only the training cost. The training cost to use the Personal Software Process ^SM to help produce 10,000 lines of code is $105,600. Table 33 illustrates the breakeven point of the Personal Software Process ^SM .

Table 33: Breakeven Point of Personal Software Process ^{S M}

SPI Method	Benefits/Costs
Software Size	10,000
Total Life Cycle Cost Hours (Testing)	45,100
Old Productivity (Testing)	0.22
Total Life Cycle Cost (PSP SM )	400
New Productivity (PSP SM )	25.00
Productivity Difference (Testing/PSP SM )	0.01
Special Costs (PSP SM )	$105,600
Breakeven Point (PSP SM )	$106,545
Breakeven Point After Project Start (PSP SM )	2 Hours

Now we are ready to determine the breakeven point of using the Personal Software Process ^SM to help produce 10,000 lines of code. Divide the special costs of $105,600 by one less the productivity difference of 0.01. The breakeven point of using the Personal Software Process ^SM to produce 10,000 lines of code is $106,545.

Finally, let's put the breakeven point of the Personal Software Process ^SM into proper perspective. Subtract the special costs of $105,600 from the breakeven point of $106,545, and divide the results by 400. (First divide by 100, which converts dollars into hours, and then divide by 4, which converts staff hours into elapsed or calendar time). This final manipulation tells us that the special costs of $105,600 will be recovered in two hours after project start. This is less than one day.