The CS616 and CS625 are the same in size, form, and function. The only difference is in the output signal. The CS616 has a ±700 mV square wave output, whereas the CS625 has a 0 to 3300 mV square wave output.
The CS625 was designed for use with the CR200- and CR200X-series dataloggers, which cannot measure negative voltages. Consequently, the output was modified to keep the entire signal in the positive voltage range.