Investment for GJTester(IG): ~1000 EUR
Total software creation effort (TE): development (D) + testing (T)

Traditional approach (testing+ implementing test drivers) (TA):
Traditional testing is 30% of the total effort

New approach (NA)
Testing with GJTester: 20% of the total effort
Let us assume a project investment
Investment (I)= 100 000 EUR
Investment tester (IT) ~ 1000 EUR
Additional effort for learning how to test with GJTester (AE) ~ 1000 EUR
Income the first year (IC) = TA - NA ~ 30000 - 20000 = 10000 EUR
Outcome in the first year (OC) = IT + AE ~ 1000 + 1000 = 2000 EUR
Benefit in the first year (B) = IC - OC = 8000 EUR
Return on Investment (ROI) = (IC - OC)/OC ~ 400%
Payback Period (PP) = (IT + AE)/B ~ 2000/8000 = 0,25 year