What does it matter if your dog gets a little more one day and a little less another? I'm sure you do with your own meals. In fact I'd add that in all possibility it's more healthy for your dog, and certainly mimics what would happen in the wild.
There is so much rubbish talked about feeding dogs, and much of it by the dog food manufacturers who have a vested interest in dog owners becoming a captive market. One of the big myths is that you must always feed the same food or your dog will get a gippy tummy. Follow this myth and it will become a self fulfilling prophecy! Feed the same thing long enough and the dog will loose the ability to process anything different. But dogs by nature are opportunist feeders. In the wild they will eat whatever presents it's self, be it what it has caught and killed, whatever carrion it finds or even nuts and berries if that's all it finds that day. The same thing can be said about a balanced diet. There is simply no need for every single meal to be balanced. As opportunist feeders it certainly would not be in the wild, but like us, their bodies are capable of balancing out over the longer term. Think about yourself. One day it might be a full roast meal, another day a salad and another day fish and chips. Not exactly balanced, but over the course of a few days, unless you are living on crazy food, your body will get everything it needs, and exactly the same thing applies to your dog.
I never weigh my dogs food any more than I weigh my own. Yes I feed a proprietary dog food, but I also add in any of my leftovers and just guess the amount of dog food to allow for the human food. As to what human foods, almost anything. Some human foods, onion for example can be dangerous in large quantities, but the little onion they will get from my leftover liver and onion is certainly not going to be enough to do any harm, so I just pick out the obvious bits. Yesterday it was macaroni cheese, today was a little gravy from my roast chicken and tomorrow will be chicken pasta with tomato and basil sauce. I started Chloe in this just as soon as she came home at 8 weeks old, just as I did with Amy and all the dogs which came before. The dogs love the variation and have rock solid digestion systems.
Regards, John