Reference is sort of like a drummer for a band. It keeps everything in sync with each other. With video things tend to get screwy if all your devices (deck, nle, monitor) are not in sync with one another. The aja
Gen 10 will do a reference for almost all flavors of video and its economical.
So with this device, you set your Gen 10 to the desired setting and feed the signal through bnc cable to the "ref in" ports on your aja card and you deck. After that life should be peachy.
Heres the wiki on signal generators, it has a a little more in depth description than i provided.
Signal Genereators. Youll be interested in the part at the bottom, sync pulse generators.