Simple multiplication with quick measure?

HI, I am a Dax M language type of person, but am able to steal and amend a few calcs here and there......This seems very complicated.....However, I do not a have grasp as an MS Access user of uniqueness and row level joins etc...... I am guessing/assuming that the column data is not tight enough, so are the rows mis-joining and not aligning properly, so rogue values are being grouped intra row? Do I need to create a calculated column and concat a load of col values to force a stronger "perfect" unique join and then apply the calc? I know thats not Dax'style or purist, as I am just looking for a dirty workaround that works that I can understand as a none programmer....? 😞...... I also get confused as to whether its better to create new tables at transfomration stage and rejoin them than apply measures after the event...... i.e. receive data, break it down into logical chunks, then glue it back together using keys etc.....(a bit like I am suggesting above?)....