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Comparison of Electronic Balances / Scales
| Scale |
i-201
|
|
|
|
|
|
|
ZSA120
|
| Made By |
MyWeigh
|
Acculab
|
A&D
|
Sartorius
|
Acculab
|
Sartorius
|
Sartorius
|
Scientech
|
| Capacity |
200g
|
210g
|
120g
|
810g
|
120g
|
500g
|
100g
|
120g
|
| Readability |
.01g
|
.01g
|
.01g
|
.01g
|
.001g
|
.001g
|
0.0001g
|
0.0001g
|
| Precision |
±0.01g
|
±0.01g
|
±0.01g
|
±0.02g
|
±0.002g
|
±0.002g
|
±0.0002g
|
±0.0002g
|
| Repeatability |
0.01g
|
0.01g
|
0.01g
|
0.01g
|
0.001g
|
.001g
|
0.0001g
|
0.0001g
|
| 3% SG Acc.* |
.41/2.1
|
.41/2.1
|
.41/2.1
|
.04/.21
|
.04/.21
|
.04/.21
|
.008/.04
|
.004/.02
|
| Discount Price
|
|
|
|
|
|
|
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*3% SG Accuracy means the lightest gem
or mineral, in grams/carats, that you can measure specific gravity on
the scale, and still get an SG with reasonable accuracy, defined here
as within 3% of actual. See Table below for more details.
Which
Electronic Scale do you need for measuring specific gravity of your
gemstones?
Use the following table to help answer
that question. It shows the Theoretical Specific Gravity Accuracy
for a typical gemstone with a SG of 3.50, such as Diamond. The
development of the table is based upon the very real premise that as
you approach a scale's minimum readability, a specific gravity measurement
becomes increasingly less accurate.
The top row of the table below lists
readabilities, in grams/carats, of 4 increasingly sensitive scales.
The left column represents declining % degrees of accuracy from actual
SG. The numbers in the body of the table are in carat weights
of increasingly smaller stones, going down.
For example, look at the colored cell
that reads 0.21. An electronic scale that offers readability down
to 0.001 grams/0.005 carats will theoretically produce specific gravity
measurements on stones weighing as light as 0.21 carats, with 3% accuracy.
Another way of saying this is that on an electronic scale with readability
of 0.001g, a diamond that has an SG of 3.50 and weight of 0.21 carats
would theoretically measure from 3.40 to 3.61, or 3% either way from
3.50. It thus follows that heavier stones will give more accurate
SG measurements, while lighter stones that "push" the minimum readability
of a scale will produce less accurate SG measurements. Read more
below the table.
Readability - Right
% SG Acc. - Down |
.01g/.05ct |
.002g/.01ct |
.001g/.005ct |
.0001g/.0005ct
|
| 0% |
15.00 |
3.00 |
1.50 |
0.15 |
| 1% |
4.85 |
0.97 |
0.49 |
0.05 |
| 2% |
3.10 |
0.62 |
0.31 |
0.02 |
| 3% |
2.05 |
0.41 |
0.21 |
0.02 |
| 4% |
1.70 |
0.34 |
0.17 |
0.02 |
| 5% |
1.35 |
0.27 |
0.14 |
0.01 |
| 6% |
1.00 |
0.20 |
0.10 |
0.01 |
| 7% |
1.00 |
0.20 |
0.10 |
0.01 |
| 8% |
1.00 |
0.20 |
0.10 |
0.01 |
| 9% |
1.00 |
0.20 |
0.07 |
0.01 |
| 10% |
0.65 |
0.13 |
0.07 |
0.01 |
The same scale with
readability down to 0.001g could also be used for stones weighing down
to 0.07 carats, although with 9% accuracy. So you can see that in
choosing an electronic scale for SG measurements, this table can be very
helpful. For most gems, a scale with readability of down to 0.01g
is ineffective for SG measurements (although adequate for most minerals
and larger gem rough). Rather, a scale with readability of 0.002g
is a minimum practical requirement, with SG's reasonably accurate (3%)
to 0.41 carats. An electronic scale with readability to 0.001g
is preferred, and offers the best value for the money, although for
stones as lightweight as 0.02 carats, an analytical scale reading down
to 0.0001g is required.
Remember that as
with most Specific Gravity measuring devices, for very lightweight stones,
you can always weigh 2 or more of them together so that their
combined weight is heavy enough to be "sensed" by the device, providing
you know that the group of stones are all from the same source.
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