Hi there!
Here are some thoughts on scales and relative value of scales. I found this information online, and you can go to
http://ask.metafilter.com/mefi/25554 for the entire thread and discussion. In accordance with forum rules, to make it easier for you, I will paraphrase just a very small part of this thread, because I think that what is said by the author (not me, unfortunately!) is really, really, relevant:
Scale" "accuracy" can mean many different things, and it might be useful to consider in more detail what you need. There are at least four different definitions that i can think of:
- stable - you put a weight on and the reading stays within some range while you look at the scale
- repeatable - you put the same weight on at different times and you get the same reading (with some error range)
- absolute value - you put a known weight on and get the correct answer (with some error range)
- precision - you get a readout to so many decimal places
for me, looking to monitor my weight (which is what i guess you might be doing too), the two important factors are stable and repeatable.
stable is tricky - if i move around on my scales, the value does change. but if i stand still and straight, it seems to be pretty stable. so i stand still and straight (no leaning over to one side to persuade it to say i'm lighter
)
repeatability with simple mechanical scales (the cheap ones) is likely, in my opinion, to be pretty good, as long as you always use them in the same place, on a flat, hard floor, and check that the reading is set to zero before use (i check my weight every day, at the same time, in the same place, and it typically varies by about a pound, so my cheapo mechanical scales have a repeatability of about that - and i am amazed at some of the reports about people's weight fluctuating from day to day by amounts much more than that, but that's another issue...)
in particular, scales often have a printed warning about absolute accuracy - that they are only accurate to +/- 10 pounds, say. but for me that's not important. i measure my weight at the same time, in the same place, with the same scales, every day, and all that matters to me is the changes. i don't really care if i weight 140 or 200 - what i do care about is whether i have increased by 2 pounds. some scales with an accuracy of 10 pounds may, in practice, be repeatable to a pound or two.
now i don't know if that's the same for you. you might be needing absolute accuracy to compare with some medical requirements, for example. but it's at least worth mentioning, because repeatability tends to come at a much lower price than absolute accuracy, and for many uses repeatability is sufficient. and unfortunately, it's absolute accuracy that tends to be reported.
also, note that precision alone doesn't necessarily imply anything else. you might find that one minute you weight 200.000 and the next, 221.543 (taking an extreme example). there's nothing to stop someone sticking a high precision display on scales with poor repeatability, or poor absolute accuracy."
The bottom line is that you might want to weigh yourself like this author does -- at the same time, with the same clothes, in the same location, with the same scales -- in order to monitor your weight. Bouncing from scale to scale, each of which will have a different range of error, will lead to FRUSTRATION, DEPRESSION, and DAIRY QUEEN. Think of your weight as relative -- that is, last week I weighed X on this particular scale, and this week I weigh X-2.5 lbs. Forget the numbers for now IF you are bouncing from scale to scale, as the relative movement is what is important.
New Scale, Different Weight
Keep up the hard work and you will see those scales/numbers go down to!
