This is a good rhythm strip to use to illustrate how atrial fibrillation can almost look regular when the rate is fast.  Students should be taught how to "march out" the rhythm for regularity.  It is always a good idea with atrial fib to take a longer strip, looking for the inevitable "gaps" in the R-to-R intervals.  Also, as your students progress, a 12-lead ECG is invaluable to really search for P waves.  Even two or three simultaneous leads are better than just one.