Hi Piiwan58,
Blood glucose meters read like yo-yos?
Well, yes, they do, but the way to deal with unreliable precision is, as Gudrun said, to squint past the noise, to look at trends over many measurements. I just took 10 readings in row spread out over 8 minutes. It was early afternoon, local time, and except for the two mugs of coffee this morning, no sugar, lightened to a dark chocolate colour with milk, I have not eaten since 7 PM last night. So my blood sugar was bound to be stable over the eight minutes it took to get the measurements. A precise meter should report 10 copies of the same number.
Here's what I got: 4.6, 5.1, 4.7, 4.4, 4.9, 4.8, 4.6, 4.6, 4.6, and 4.7. Now I'm not recommending burning 10 strips to get a reading. But meters, like all measurement tools, exhibit measurement error and it is up to us to discriminate real differences from noise. If you take regular readings under the same conditions, as in morning fasting readings, look at the trend over weeks or months. Plotting really helps, I think, as the eye readily picks up an increasing or decreasing -- let's hope -- trend. Take a look at my own chart if you will:
http://web.ncf.ca/fx536
There's a saw-tooth pattern that corresponds almost perfectly to readings taken after a day of fasting compared to a day of eating. The meter is properly tracking. (But a margin of error has to be imagined to bracket each point.) It's important not to be alarmed over a half point up or thrilled about a half point down on a single reading. (Although I confess to having done both.) Like the 5.1 and 4.4 in this series, there are random discrepancies that we can appreciate by looking at the overall picture.
The imprecision has an important implication for food diaries. I'm not compiling a food diary, but if I were to do so, I would take readings of the same meal on several occasions before deciding to remove or to consume more of any particular food. Starting off in guiding food choices, it would be better to use existing tables of glycaemic indeces and glycaemic loads for a first approximation rather than to rely on a single reading from a home meter. Then, once a particular food has been measured for its impact on your bloods a few times, you can base your consumption on readings instead of tables, and thereby tailor food choice to your reactions.
Meters are imprecise, and likely to be inaccurate too, but are they useful? Oh yes. One just has to know how to use them. Getting a meter was the best thing I've done for myself.
Best of luck in exploring what works for you,
George 1951