COMMENT: I am using this calculator to determine the value of a wedding gift I have to give relative to the gifts I referred when I got married. The site is very educational and should be required as part of economic classes in schools.
RESPONSE: Your use highlights one of the most important points of measuring relative worth, and that is there is nearly always more than one relevant answer. If you are looking at the wedding gift you received many years ago, you could be thinking about how much it “cost” you in the share of income you spent. You would use the income or labor value for that.
But if you were thinking about how it “ranked” with other gifts you received, was it the most expensive or was someone giving you another cheap salt and pepper set, then you would use the real price index.
Thank you for your compliment and, of course, we feel economics classes should learn more about how to compare relative worth.