How To Calculate Percent Off Center?

This came up in another thread and I thought it might be worthwhile to start a thread on the topic.

There are two schools of thought as to how to calculate the percentage a coin has been struck off center:

1) Measure the distance the coin has been struck off center (e.g., edge of coin to edge of where the die struck the coin or center of coin to center of the design) and divide that by the diameter of the coin then multiply by 100.

2) Divide the area of the unstruck portion by the total area and multiply by 100.

The two methods give very different results. For example, assume a coin was struck off center such that the center of the die is exactly at the edge of the planchet (and the edge of the die is at the center of the planchet).

If you calculate the percentage off center using method 1 you would say the coin is 50% off center.

However, if you calculate the percentage off center using method 2 you would say the coin is much more than 50% off center, perhaps 65% to 70% off center.

So which is the "official" way to calculate the percentage a coin has been struck off center?

Please indicate whether you know the answer or whether you just think your method is correct. If you know the correct answer please provide a source (if possible).

 

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I don't know the correct answer, but I THINK the most logical answer should be the distance from edge of planchet to edge of strike compared to original planchet diameter. Just my two cents.

 

I knew that one person was going to make a thread on this:thumb:

 

It is calculated by a line through the center of the coin from rim to rim. For example, if you have a coin that is 1" in diameter, and it is 1/4" O/C, it would be 25% O/C.

The easiest way to calculate the percentage would be to use a set of calipers; measure the diameter of the coin (preferably in millimeters); measure the distance off-center, and divide the off-center distance by the diameter.

Chris

 

This is how I Think it is calculated. From the middle of the coin edge where the coin is off-center (1 on illustration, below) at use that as your starting point. Directly bisect the middle of the coin edge where the edge of the coin image starts showing on the planchet (2 on illustration). And finish that line at the opposite end of where you started (3 on illustration)

Then figure out percentage away from the origin point (0 percent) to the opposite end (100 percent). If the starting of the struck area is halfway up the planchet, it's 50 percent.

 

I don't over think nuthin'. Out comes the elementary school protractor........

 

I am 90%+ sure kasia is correct. I have never seen the answer in writing, but in this example http://coins.ha.com/c/item.zx?saleNo=1169&lotNo=12253, I can guarantee that the impression is at 45% of the diameter (measure) and it is much less than 45% of the area.

 

You go girl.......

 

That is the way I always thought it was done but a few years ago an error "expert" told me the proper way to calculate percent off center was method #2 (above). That is the reason I started this thread - to determine the "official" method.

I'm going to the ANA National Money Show in Denver this week. I will ask around and see what I can find out.

 

Hopefully Fred W. will be there. I believe he would have a good idea.

 

The first method is the only one I have ever seen used. It just makes more sense to go by distance instead of area.

Looks like NGC uses method #1 too
http://www.davidlawrence.com/inventory/viewitem.cfm/inventory/205457/inm/No-Date-Roosevelt-10c-90%25-Silver,-50%25-Off-Center-NGC-AU58/snm/Roosevelt-Dimes/gnm/Half-Dimes-%26-Dimes/lotid/312445

 

Dang dude, is it the bourbon or are you facing (avatar) the wrong way?

 

Yes, the coin is the wrong direction xD. I'm surprised it took so long for someone to say something about it. but the actual coin is normal, I just flipped the image in photoshop.

 

Thank the Lord. I was almost ready to give up the bourbon.......

 

Quit talking so silly.

 

I'm starting to wonder how much he's actually had. He's been making silly posts on other threads too

 

But I'll be sober in the morning......

 

A few decades ago, I was fortunate enough to attend some basic math seminars at Cal Tech. The one that stuck in my mind was the "new idea" of measuring the area of an wierd shaped plane. They simply covered the area with a grid and counted the squares. They simply rounded off the squares that were only partly filled by area of the plane. This was at all the perimeter, of course.

The smaller the grid sections, the more accurate the measurement.

So why not cover the coin in question with a grid. Maybe even the one on the MS Paint program ? Count how many squares are covered by a perfect coin. The next grid would be over the offset one. Count the squares of the unstamped (or stamped, I guess) to determine it's area. Then you could determine very closely how much of the planchet was actually stamped. That area divided by the area of the whole planchet would give an accurate percentage of offset...........I believe.

Say the entire planchet has an area of 300 by your grid measurement.

The unstruck portion of the planchet has an area of 50 by that same sized grid.
The struck portion of the planchet is now 250 grid squares.

250/300 = 83%.................so, couldn't you say it was offset by 17%, since only 83% of the strike was made ?

Seems an easy way to determine it to me ?

gary

 

However you do it what you are describing is Method #2 (above). I think your way would be fairly accurate (and get more accurate as the size of the squares gets smaller).

I hope to get an "official" answer to my question at the ANA show this week.

 

I like the look at it and guess how much it is off