Why is your weight reading best shown when you stand at rest on the scale?

I am not sure I know what you are asking? do you mean the scale like you find a doctors office? If so, measure height by extending the ruler up higher than the person you are measuring. Have the person stand with their back to the ruler, lower the ruler until the flat part is sitting on top of their head, and record the corresponding number on the ruler. As for the weight, use the balance. Move one weight at a time starting with the heavier weights (usually in 100lb increments) If the scale tips, put that weight back one notch and continue with the smaller weights until the bean rests level.