Is it possible to synchronize two NI USB-9162 chassis?

First of all is this question in the right location? Or should I post it to signal conditioning? Anyways I am attempting to collect voltage differentials using two NI USB-9162 Chassis, one with a NI 9215 module and the other with NI 9219 module and i am getting wierd results when I write the measurment ot a file. Any hellp would be greatly appreciated!

Thanks