I use telescoping gauges and a digital caliper. you could use a micrometer at that point or a dial caliper, whatever you want. The measurements will only be accurate if you use them properly and have an acurrate measuring instrument.
http://www.bsbridge.com/TelescopicGaugeABCDEF.jpg
Before you start spending on measuring equipment think about what you want to do. You can measure out your block all you want, but if you are going to take it to a machinist your measurements won't mean crap. He's going to check everything himself regardless and give his opinion. If you are just going to be sticking stuff together or doing most of the work yourself it can be helpful to know where everything is at.
I generally measure cylinders at 6 points. Top of the bore below the ridge perpendicular and parallel to the crank, middle of the bore perpendicular and parallel to the crank, and the bottom of the bore perpendicular and parallel to the crank. Doing this you can see how out of round and tapered the cylinder is. Thats how I was taught to do it.