Do Diminished Value Calculators Work? In the last few years, many Diminished Value Calculator scam sites have popped up all over the internet claiming to have an automated system to determine Diminished Value. Many of these systems use a variation of Formula 17C which was developed by Insurance Company but which has since been shown to be flawed. Insurance companies love this formula because it normally works in their favor and can cost you thousands. There are some other calculators which provide inflated values and again are not considered credible.