specifically how are off centers measure for percentage?
krueger
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seems folks are using eyeball estimates.
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krueger
Posts: 901 ✭✭✭✭
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There was something called a Kolit gauge which was used to both specify the direction in which a coin was off center and to determine the percentage. The directional gauge was like a clock, it is why many old time collectors will refer to positions on a coin as "K-8" or "K-10". The off center gauge was a series of arcs showing the area of a struck coin in 10% increments. The same gauge could be used to determine the amount of material missing in a large clipped planchet.
A couple of quick GIS didn't turn up anything, but I know I have seen them reprinted in books and catalogs before, so hopefully someone will wander by and add them to the thread.
Sean Reynolds
"Keep in mind that most of what passes as numismatic information is no more than tested opinion at best, and marketing blather at worst. However, I try to choose my words carefully, since I know that you guys are always watching." - Joe O'Connor
The process for exact calculation of off-center coin percentages is in the John Reich Journal article September 1995 by Russell J Logan, "Off-Center Bust Half Dollars: A Definitive Description." Logan uses integral calculus to derive the area within a circle. This article can be read on the Newman Numismatic Portal.
Coin diameter is 10mm.
Edge of design is 3mm from edge of planchette, then you’re 30% OC.
Pretty easy measurement and arithmetic.
This was sold in the 80s good idea.
So % is by diameter and not area. For some reason I always thought it was by area.
It is hard to judge by how much of the design is showing because the planchette will expand beyond the original diameter when struck off center. I always estimates by how much area of the planchet was unstruck, which the pictured gauge can help you ascertain.
Sean Reynolds
"Keep in mind that most of what passes as numismatic information is no more than tested opinion at best, and marketing blather at worst. However, I try to choose my words carefully, since I know that you guys are always watching." - Joe O'Connor
Link to the article
Below is Logan's table for finding the area from the diameter percentage. As he points out, a close approximation can be made by multiplying the diameter percentage (the "linear ratio") by 1.2 which will yield an error of less than 2% for all strikes less than 65% linear (which is pretty much every off-center strike).
Lance.
Funny story...after some collector complained that his coin was off-center by 21% and not just the 20% assigned, the TPGS stopped putting a % on any more coins. Enough of this nonsense! Now, AFAIK, that's the way it is, Off-Center Period.
Technically this isn't correct but I measure the OD along the off center direction, then measure the distance from the edge of the the off center to the initial edge of the struck field. Divide and that's the percentage off center. Not exact but probably within a couple percent. Plus the math is easy
Well at least PCGS does. Good for them. When was this one slabbed?
Yes, by diameter.
Just to illustrate how much of a difference this makes, take two ordinary quarters. Lay one on the table and pretend it is a planchet. Now lay the other one atop it half way off to the right and pretend this is the strike. The 50% of the “planchet” to the left of the “strike” is blank, plus large curved areas above and below the “strike.” Thus the “strike” is 50% off by diameter but roughly 70% by area.
Thanks. I learn something new every day. Up until now I figured a "50% clip" meant half the area of the coin was missing. Now I know better.
Well.......... I have seen clips measured by both diameter and by weight, the latter of course being a measure of area.......... Either way is acceptable so long as labeled.
Not being an error collector, this is interesting.... Learned something new today....
Cheers, RickO
I consider it a visual approximation of how much design is missing along with how much planchet is showing. There are factors which make turning the "percent off-center" into a "science" pretty difficult, such as a uniface reverse can cause a long "slide" in the design off the planchet. Other combinations of other error types with an off-center also can make it difficult to be precise (e.g. an off-center on a major curved clipped planchet.)
The best way in my opinion is to look at the design missing, planchet showing, and approximate between the two.
I like this coin, but I’m holding out for one at least 18% off-center.
Russ Logan's article probably never made it beyond the small world of the JRCS to the larger base of error collectors.
Logan took a complex calculation and simplified it to an easy formula with an error margin of no more than 1.7%. Simply multiply the linear ratio (difference/diameter) by 1.2, to get a very accurate off-center percentage in area.
@FranklinHalfAddict
Using the linear formula answer of 30% greatly understates the actual off-center percentage of 37.6%. Using Logan's simple formula gives an answer of 36%, an error of only 1.6%.
Here is the page with Logan's formula in table form. It is easy and gives a much more accurate answer. This formula is what should be used by error collectors and TPG's to give consistent and accurate off-center percentages:
Here is the link to the Logan JRJ article on the NNP https://nnp.wustl.edu/library/book/529763
For Off Centers, I just eye them if there is not a percentage on the slab. Not hard to be "fairly" accurate.
For Clips, I weigh them (raw coins) to be 100% accurate.
@Insider2
Why not state a percentage off-center with the Logan formula, when it is easy, consistent, and very accurate?
I personally just use my eye and round to the nearest 5%.
About ten years ago, at the ANA Coin Camp YN auction, I purchased a lot described as
"1793 Wreath Cent Superb Gem 100% off-center strike"
Maybe I paid $400.
The next year I bought a "1793 Wreath Cent Superb Gem 100% clip"
Paid about the same.
The next year one went for less because I already had cufflinks
As much as I treasure each of them, I sometimes still get them mixed up
@MrEureka and I are making a market in the most common gold error, off-center Indian $2 1/2.
Our buy/sell is 2.7%/6.6%.
You wouldn't happen to have any coins that have been seared would you?
Is this the ANA instructor who punked me in the infamous coin-searing incident?
It's been too long since I have seen you. Maybe in Chicago?
PM sent
I use my eyes fo most 5-10-15% Off Centers,
but believe it or not, I use a ruler almost
all of the time.
I measure the amount of Blank area on the
off center strike, vrs. the diameter of the coin.
And, as the Captain says, I round up or down a
bit - or, if I really can't decide if a coin is 15% or
20% off center, I have used a middle number,
like the quarter above - 17% -
I try not to use the middle numbers often, so
they are very few and fair between.