For my boys that won't hold still I just shut them in there with a few treats, usually in the time it takes them to sit quietly and eat one yogie I can get an accurate weight. The first few times they were a bit "huh? what is this? lemme out!", but after the first few times they've gotten used to it. Does your vet have a scale that he fits? If so you might ask them. Or what about a large dish? I mean like a serving platter type thing, big enough for Oscar. If he would sit quietly on the scale for you, he might sit quietly and still on some sort of dish, especially if it wasn't closed in like a box.
edit: Sorry, I guess none of this really answers your original question of what scale does everyone have. I don't know off the top of my head.