I weigh myself every Friday morning after I get up. Over the past few weeks, my weight seems to be constantly fluctuating: one week, I've lost 400 grams, the next week I've added a kilo, and so on. This has been mildly depressing as I seem to be generally gaining weight, despite the generous amount of exercise that I've done over the past few weeks and the little that I've eaten.
This morning I was very happy when I saw that my weight had dropped to 78.4 kg, which is the lowest it's been in years. But my happiness was tempered by the perplexing discovery that apparently I had lost over a kilogram in the past week - perplexing since I have stopped swimming and I didn't walk three nights in the past week. While walking the dog, I considered the possible reasons for these fluctuations. My first thought was that I was misreading the digital scale - possible with the way my eyesight is at the moment; I could be confusing a 9 with an 8.
But when I got home, I decided to try an experiment: I weighed myself in one room then I weighed myself in another room. The weight should be the same, no? No! There was a 600 gram difference between the two measurements! How can this be? The room with the lower measurement is part of the original building, whereas the higher measurement was made in the room which was added as an extension ten years ago; this extension is not actually connected to the original building (there are subsidence problems which are due to the house being built on a hill). I suspect that all the lower measurements were made with the scale in the original building, and the higher measurements in the extension.
Now being aware of this, I am always going to weigh myself in the original building. From my work as an analytical chemist, I know that scales should not be moved - but those scales are laboratory scales with a different order of sensitivity: they can measure milligrams but certainly not kilograms (probably not more than 10 grams). But the general idea still holds: always weigh oneself in the same place, at the same time. As far as my weight is concerned, the absolute measurement is not too important; it's the change from week to week that counts. In other words, it doesn't matter too much whether I weigh 78.4 kg or 80.0 kg at the time of measurement; it's more important to know that during the week I lost 600 grams (or whatever).
The digital scale in the clinic is supposed to be the most accurate, but the only way to get a true reading would be after a blood test (prior to which I wouldn't have eaten or drunk anything for twelve hours) and naked. The first condition is easy to obtain, but the latter is getting more difficult as the days become colder and I wear more clothes.