I'm trying to institute a formula that will calculate the difference between some rows. The sticky part is, I need to find the difference from the greatest update date (which will always be at the bottom of the set) from the smallest update date (which will always be at the top of the set.

Type Entry Type Weight Weight Change Expectation Cat Initial 110.00 0.00 0.00 Cat Update 105.00 -5.00 -5.00 Cat Update 102.00 -3.00 -8.00 Dog Initial 175.00 0.00 0.00 Dog Update 172.00 -3.00 -3.00 Dog Update 170.00 -2.00 -5.00