Eliza -

For those who need something beyond the small stock scale, many truck stops in the US have "pay to weigh" scales so that truckers can check their weight before they cross the state line and hit a weigh station. (A couple of bucks gets you some assurance, and the fines for being overweight can be $$$$$$ - hundreds.)

The real question here is how one decides whether the scale is inaccurate. A daily variation of a few pounds is fairly normal for most people, which is one reason the diet docs tell them not to weigh themselves more often than once weekly.

When I explained to one friend the method for "wiggling the scale to zero" and adjusting so that was where it said zero, this one person developed a technique of "steadying the hand" with a thumb on top of the scale while turning the knob, thus making the "zero" indication actually at about 2 or 3 pounds, and began reporting a "significant weight loss" since her scale thus indicated a couple of pounds less than actual.

Our group, for a while, called the little adjustment knob the "liar button" in her honor.

"Diet scales" for weighing food portions generally have a very simple "zero adjustment" so that you can put the plate on, zero the scale, and then add the food to get an accurate meausre of how much you've prepared.

Dial type "Kitchen thermometers" of the kind you stick into the meat nearly all have a "zero adjuster," often requiring a wrench that sometimes is built into the "sheath" they store in, to "turn the dial." If you haven't "set to 212F (100C) in boiling water" these thermometers are extremely variable - and inaccurate - "off the shelf." For some unkown reason, few people seem to be aware that you can "set them right."

John