Measuring Devices

[sarab]

Hi,

Are plastic calipers sufficient for accuracy?

I do not own any measuring devices, but am considering them.

Thank you.

[Steph]

Plastic calipers are perfectly acceptable for most purposes.

Better plastic than metal for measuring marbles.

I've thought about getting one of those fancy calipers which measure to the thousandth of an inch, but you can do quite well with a basic plastic set.

[hdesousa]

Hi,

Are plastic calipers sufficient for accuracy?

I do not own any measuring devices, but am considering them.

Thank you.

Plastic calipers are accurate, and precise to 1/128 of an inch, when using the vernier scale.

http://www.physics.smu.edu/~scalise/apparatus/caliper/

Can probably find them on line for less than a couple dollars, post paid. Best bang for your buck.

In the description below, if you'd rather measure in inches instead of centimeters, use the top scale.

Vernier Caliper Instructions on use

• The Vernier caliper is an extremely precise measuring instrument; the reading error is 1/20 mm = 0.05 mm.
• Close the jaws lightly on the object to be measured.
• If you are measuring something with a round cross section, make sure that the axis of the object is perpendicular to the caliper. This is necessary to ensure that you are measuring the full diameter and not merely a chord.
• Ignore the top scale, which is calibrated in inches.
• Use the bottom scale, which is in metric units.
• Notice that there is a fixed scale and a sliding scale.
• The boldface numbers on the fixed scale are centimeters.
• The tick marks on the fixed scale between the boldface numbers are millimeters.
• There are ten tick marks on the sliding scale. The left-most tick mark on the sliding scale will let you read from the fixed scale the number of whole millimeters that the jaws are opened.

  

• In the example above, the leftmost tick mark on the sliding scale is between 21 mm and 22 mm, so the number of whole millimeters is 21.
• Next we find the tenths of millimeters. Notice that the ten tick marks on the sliding scale are the same width as nine ticks marks on the fixed scale. This means that at most one of the tick marks on the sliding scale will align with a tick mark on the fixed scale; the others will miss.
• The number of the aligned tick mark on the sliding scale tells you the number of tenths of millimeters. In the example above, the 3rd tick mark on the sliding scale is in coincidence with the one above it, so the caliper reading is (21.30 ± 0.05) mm.
• If two adjacent tick marks on the sliding scale look equally aligned with their counterparts on the fixed scale, then the reading is half way between the two marks. In the example above, if the 3rd and 4th tick marks on the sliding scale looked to be equally aligned, then the reading would be (21.35 ± 0.05) mm.
• On those rare occasions when the reading just happens to be a "nice" number like 2 cm, don't forget to include the zero decimal places showing the precision of the measurement and the reading error. So not 2 cm, but rather (2.000 ± 0.005) cm or (20.00 ± 0.05) mm.

[sarab]

thank you both!

LandOfMarbles offers a couple dollar model caliper and I'd like a little pocket size black light. The light really can show the truth in things.

I also posted my pics of my marbles on my personal FB page and it's so cool, some of my friends with 'jars of marbles' are coming out of the woodwork! Indiana will be the marble state!

[SNYD]

Go to Lowes, they have very nice ones that are plastics that measure in fractions of an inch ( which is great) or decimals or metric. They give actual fractions so you do not have to count lines or figure decimals. They are small too which is nice to carry in pocket

SNYD

[hdesousa]

Genius:

http://en.wikipedia.org/wiki/Vernier_scale#mediaviewer/File:Using_the_caliper_new_en.gif

[Steph]

Now that's cool.

I had no idea about that function.