Thanks for your reply Robin!
You asked "Does it miss steps?" It misses microsteps. I think for every 8 microsteps, it hit-or-misses several. But by the end of 8 microsteps, it has caught up, having produced the equivalent of an accurate full step.
I am using an 18V variable 3A bench supply. I started at 12V (which the motor is), but have gone higher. The bench supply has a current meter.
I having adjusted the pot on the Easy Driver board, but I have noticed no significant effect on the microstepping "problem". Current doesn't seem to exceed .6 A on the bench supply meter.
Maybe this is as good as it gets for microstepping with the motor and Easy Driver?
I also have a 2A bipolar stepper motor and a Big Easy Stepper Driver. I may prototype that with the Arduino and see what kind of accurate microstepping I get in that case.
Mark