The only truly accurate scale is a balance scale, assuming the weights it uses are accurately made. Any spring scale, including those fancy high-tech digital ones that have replaced balance scales in a lot of doctors’ offices, is inherently less accurate, because the spring is much harder to calibrate. If you’re lucky, your gym has still retained its balance scale.
So that means that, first of all, two spring scales, no matter how carefully calibrated, are not likely to match. The best you can hope for is that their measurements will rise and fall consistently together. You might never know which is the “real” reading, but at least you will know trends. We used to have a scale that consistently measured my weight about 30-40 lbs. (13.6-18.2 kg) lower than it really was. Now we have a scale that consistently tells me I weigh about 100 lbs. (approximately 50 kg) less. I know my true weight from using the balance scale at the gym. It’s a cheaply made scale, but accurate enough for my purposes.
So the question is just how much you want that number to mean to you. Do you care more about achieving a particular weight, or about losing inches around your waist and gaining metabolic health? Would you rather look as though you’ve lost thirty pounds, say, or lose those thirty pounds and still look just as heavy?
By the way, that scale that measured my weight as 30-40 lbs. less? I could get it to read anywhere within an 80-lb. range, just by how I stood on it. And if I measured the lowest weight possible three times in a row (I mean with no more than a few seconds between the different readings), I would still get weights that could vary as much as 20 lbs. Now you know why I gave up on scales and use the tightness of my belt as my guide, instead.