Mouse roll jumps in program monitor

I NEED to be able to scrub the program monitor with my mouse roller one frame at a time (like when it does in the grey area below the video) not do this insane, chaotic jumping I never asked for and can't even begin to understand or control and totally don't want to understand it. How switch it so I can set my mouse roller over the program moniter to one frame at a time? This way I can move the mask right away and not have to move the mouse down and back up again to move the mask, then back down again to scroll. This is hell. I keep accidently rolling over the video and jumping away and having to reorientate. Please tell me how to change it. I swear it didn't use to jump around like this. This is really disrupting my workflow.