Our ones vary a kilo every time you stand on it.
My bike is either a biffer or a racer.
We need them to be quite accurate for our holiday luggage but mostly just to say the same weight if we stand on them 5 seconds apart.
Currently we are doing average of 3 readings.
Are there good ones for under £30.

Calibrate current scales with some dumbells?

For weighing luggage or bikes, wouldn’t it be easier with something you can hang the weight from?
eg a spring balance. Though not sure how much you’d have to pay for a good one.

Being limp wristed I struggle to lift a 32 kg suitcase and look at the dial on one of those fishing type luggage scales