If you don’t measure your crimp fitting—after you crimp a hose and you don’t measure it—you could get lucky; if you set up your machine properly and it’s calibrated, it probably will be very close to that every single time. In many cases, the tolerance is plus or minus eight thousandths of an inch. You could crimp it from 1.027 to 1.043.
Anywhere within that range, the hose is still valid, but you don’t know where you’re at. You either risk over-crimping and restricting flow or damaging the braiding on the hose, or you risk it not being crimped enough and blowing off a hose end.
For the cost of one of these calipers, there’s really no harm in going and buying one for $10, $15, $20 to make sure that you’re not responsible for hose failure.