FWIW most medical types don't even measure centimeters. They measure finger widths, multiply them by two, and then call them centimeters sounding very precise and scientific. And, yes, the fingers of my old 4'9" midwife are considered as much 2cm as the fingers of a 6'8" male Irish ob-gyn I met.
Personally, I found it easiest to check squatting in the tub or shower. How easy it is depends on your body and hand measurements, flexibility, and how the baby lies. When I was pregnant with my first I could barely reach down to pat the urine dry... while I was fatter with subsequent pregnancies, the babies were positioned in such a way I could easily reach my fingers up for a cervical check.
I second (or third or fourth) that dilation can change rapidly. With my last I had two contractions over a five hour period. When I went to the bathroom from the corner of my eye through the mirror, I caught a glance of a bulge in back above my pelvis. I checked and I was at 4cm. I told my dh who told his work buddy on the phone. Stupid father of two told my dh, "Don't worry. You have hours to go." Foolish dh repeated it to me and I snapped for him to get off the phone. Two contractions and ten minutes later we had our sixth child.
(BTW, I'm justified in saying *foolish* dh because my previous two labors were 7 and 2 minutes.... foolish dh!)
~BV, always feeling justified in ragging on dh during labor