@SailorJerry - For one thing, I think you probably have to have *very* high levels of calcium for it to really keep you from getting enough manganese. Remember, this is trace mineral; a little goes a long way. Load up on it and you'll wind up with manganese toxicity!
Also keep in mind that the USDA recommended level of calcium assume that you eat a whole lot of animal protein (their website admits this straight out). Animal protein inhibits the absorption of calcium - ironic, since the the message is always to get your calcium from animal-protein-laden dairy products!
So if you do not eat as many animal products as the average American, you don't need as much calcium. You could try, for instance, putting almond milk on your cereal instead of dairy milk. It has more calcium and won't load you up on animal protein.