Re: Re: what instrument is used to measure mass?

Dear Nicole:

I hope this helps.

In the following website  http://www.allmeasure.com/Measuring_Devices/Weight_Mass/Scales___Balances/s
cales___balances.html

We read: Scales and balances are used for measuring weights and 
determining mass. 
Crane scales are useful for determining in-process weights of materials. 
They are mounted in line with the hook. Mechanical units with a 20,000 
pound capacity cost in the $1500 range with an accuracy of +/- 0.5%.  
Electronic versions are typically accurate to +/- 0.1% with the cost of 
about $3500 for a 10,000 pound capacity unit. A variety of spring based 
hanging scales are available to capacities of 400 pounds.  Generally 
speaking, the scale should be selected based on accuracy rather than 
capacity (obviously overloading scales is a poor and unsafe practice).  
Accuracy is generally reflected as a percent of capacity, so there are 
more actual pounds of error associated with a 400 pound scale as opposed 
to a 100 pound scale. Considering the average item to be weighed and 
selecting a spring scale of twice that capacity is generally 
satisfactory.  A 50 pound capacity scale with 1/2 pound graduations costs 
around $50 while a 400 pound unit with 1 pound graduations would be around 
$200. The top loading spring scale is still commonly used in the kitchen. 
These typically have a separate top pan and capacity of around 10 pounds.  
The typical bathroom scale used to be primarily a spring type scale, but 
they are gradually being replaced with new electronic module units. Beam 
Balance Scales rely on a comparison between a known standard and the 
material to be weighed to produce a reading. The known standard is 
generally a sliding or series of sliding weights that are moved to balance 
out the weight of the material in question.  These are much more precise 
and accurate that a spring based scale. They are used in schools, 
laboratories and at home for hobbies. Capacities are typically much 
smaller than spring scales with around 600 grams being typical and 2600 
grams being maximum. The costs range from $100 to $200. There are still 
many high precision balances in use in laboratories.  While they are 
mechanical, provided they can be calibrated they are quite satisfactory. 
They will typically have a visible pan behind sliding doors to keep drafts 
and particulate away from the system.  The pan is linked to the comparison 
assembly which is commonly out of site. Scales can be selected depending 
on the quantity of material to be weighed.  Electronic scales are 
typically fitted with a load cell or strain gage. As weight is applied, 
the tiny resistance of the load cell changes and weight is determined by 
electronic modules. There are a wide variety available from the scale 
around the bathroom to the balance in the laboratory. Scales that are used 
in trade (selling things by weight) need to be certified and the 
electronic units are far easier to certify. The costs for electronic 
scales are a function of their capacity and accuracy.  A bathroom scale 
typically costs less than $150.  A 20 pound commercial “Legal for Trade” 
unit with graduations of 0.01 pounds costs in the $300 to $400. Counting 
Scales (determining number of pieces in a container based on the weight) 
in the 100 pound range with .01 pound graduations cost approximately $1000 
range. While precision laboratory balances with 200 gram capacities and 
resolutions of 0.01 milligrams cost about $4000. Then there’s the mass 
comparator for ultra-precision. These go for around $20,000 with a 
capacity of around 5 grams but precision in the microgram range. Of course 
you need to make your own judgments regarding the calibration of scales 
and balances.  If you are working in high precision at least look into 
calibration by an A2LA certified laboratory.  Consider all of you costs to 
do it internally using traceable standards and prescribed methods and 
compare that to the outside cost. Calibration Masses are used to calibrate 
or set scales to a true reference value.  They are available in several 
classes.  Class 1 is for high precision balances,  Class 6 for scales and 
dead weight testers, Class 7 for rough weighing applications, Class F for 
checking “legal for trade” applications and Class M2 for educational 
applications and low accuracy scales. The % of error varies by class as 
you might imagine with the Class 1 being the most precise.  Costs for the 
masses varies based on class and the number of units in the