The so–called "synchronization" means that the frequency of the strobo is consistent with the RPM of the specimen; owing of the hallucination of the eyes, the operator will find the marks on the specimen seem to be still (see Fig. 2.2). If the marks overlap, it means no synchronization (see Fig. 2.3).
※Please notice that sometimes the "false synchronization" will occur because of the visual hallucination, that is, when the RPM of the specimen is just a multiple of the strobo, the marks on the specimen will also show the still condition as in Fig. 2.2. An example is given in the following for better understanding:
Given that the RPM of the specimen is unknown, press the (14) RPM setting button and adjust the (6) RPM dial to 900 RPM. If the marks on the specimen show still as in Fig. 2.2, then adjust the (6) dial to the multiple of 900 RPM → 1800 RPM; if the marks overlap (as in Fig. 2.3), then it can be made sure that the RPM of the specimen is 900 RPM. If the marks still show motionless (as in Fig. 2.2), this means the 900 RPM is a "false synchronization". Then adjust the (6) dial to 3600 RPM; if the marks are found to overlap, then it is sure that the RPM of the specimen is 1800 RPM. The rest can be deduced accordingly.
To sum up, if a certain RPM value shows synchronization (still) and the double of this RPM value doesn't synchronize (but overlaps), then this is a real RPM value.