If you only want to measure the case, buy a digital or dial caliper. The dies don't come with a case length gauge that I'm aware of.
Or are you talking about case trimming? If so: You need to buy the cutter and lock stud (they come together), then buy a case length gauge/ shell holder combo for each different cartridge you want to trim. Here's some pics and an explanation: http://www.cabelas.com/spod-1/0003098.shtml