FMF - Friends of Minerals Forum, discussion and message board

[Jordi Fabre]

Per request of Cascaillou I'm opening this new thread in order to let the people ask questions about some detail or share any ideas about potential improvements of the current design of the topic DIY Specific Gravity Kit (tutorial) - (19)

As that topic was a kind of tutorial, I saved it in the section Featured Columns of FMF and I locked the topic in order to keep it coherent, because we will add this topic to the Asking: "What is this? / Where is it from?" reference's thread.

Please, go ahead and discuss here with Cascaillou everything you want related with the DIY Specific Gravity Kit (tutorial) - (19) topic!

[cascaillou]

the DIY specific gravity kit tutorial is now updated with some error calculations I made as to how accurate will be the obtained SG measurement depending on stone weight and scale accuracy.

However, here's a table suggesting significantly lower errors than what I calculated:
http:(slash)(slash)www(dot)mineralab(dot)com/Comparison.htm#SG
(see table down the page, beware that the weights in this table are expressed in carats, 1ct=0.2g).

I'm currently trying to reach the author of this table to discuss how he established these error values and I will report whatever comes out.

Now if anyone here has good knowledge of how digital scales operate I'd be glad to debate it.

For instance, in the case of a 0.002g scale, my calculations were based on the idea that the maximum error in the obtained SG measurement would result from from a -0.002g error in the "weight in air" reading, and a +0.002g error in the "weight in water" reading. If that makes any sense.

These are indeed important considerations, as any scale has limitations and you need to know how far you can trust your scale to yield reasonably accurate SG measurements.

By the way, when it comes to scales, you get what you pay for. For a quality pocket scale or portable scale with 0.001 or 0.002 readability, expect it to be around 200$, at least.

[cascaillou]

additional note:
I tested my Tanita 1230 scale with a 20mg weight (class E2) through a serie of 30 weighings, trying to induce error by proceeding less than carefully.
The scale proved to be right on spot most of the time, or occasionally off by -0.002g.

Very satisfied with this scale!