Remember before you post online any group that you shot. Subtract half an MOA out to 500 yards and 1 MOA between 500 and 1000 yds. (Joking)
It really depends how technical you want to get with it. If you are shooting a factory gun and factory ammo, a cheaper caliper like "Temp9" above recommended will be totally fine. Or even a ruler. If you are going to work loads, then you want something a bit better. If you have a custom set up and handloads then the Target Precision Calculator is nice. Especially to see change over time.
Unless you are punching 1 hole groups, ie 100 yards benchrest stuff, where you are tweaking your loads in your trailer up or down by clicks on your powder based on barometric pressure and temp, I wouldn't spend $100 on a set of calipers. I would save the funds, get some neck turning equipment or spend the money on better bullets, dies etc. I have shot the benchrest game and while it can be entertaining its a lot of time and money. Calipers never got guys into the prizes (well they did if it measured their tiny group). What it came down to was good dies, brass, bullets etc.