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I asked for a simple explanation for those of us who are not mathmatically inclined of ppm.  Here are some that I think are easy to understand.

Basically, if you took the product and weighed a certain amount that equaled one million grams or one million of anything, only 20 of that million would be the offending grain.  So if you had one million pennies, only 20 would be bad.  That is an infintisimal amount.  

You would have to eat a great deal of something to obtain the amount that is said to cause a reaction (1/8 to 1/4 teaspoon of gluten).  Say the 1,000,000 were teaspoons.  Divide this by 8 and you will find how many 1/8 tsps. or 125,000 1/8th tsps are in 1,000,000.  If 20 parts are gluten, then 124,980 1/8 tsps are left.  That equals 999840 teaspoons that are gluten free.  (3 tsp = 1 tbsp.  3 tbsps = 1/4 cup.  4 x 1/4 = 1 cup.   So you would have to eat 27773.33 cups of the product to obtain 1/8 tsp.  Sounds pretty safe to me.

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Cecilia, 

The example I usually use to explain it conceptually to people is that two drops in a barrel of water is about on part per million.  This also means that one drop in 500 barrels of water is about one part per billion! 

Fred
      Frederick P. Fendt, P.E. . Distinguished Engineer . Energy Systems and Pollution Abatement . e-mail: [log in to unmask] 
      Engineering Technical Center . 3100 State Road . Croydon, PA 19021 . phone: 215.785.7661 
      Houston Engineering . 6519 La Porte Freeway. Deer Park, TX 77536 . phone: 281.228.2579 
      "The opinions expressed in this email are the opinions of the author and may or may not represent the opinions of the Rohm and Haas  

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I am a last-year medical student and strive to be adept at using layman's
terms to explain what is going on to my patients so I will take up your
challenge--a simple explanation of PPM. PPM is a ratio, much like a
fraction. Example: 1/2 means that of two possible parts, one part is
present. For PPM, that lower number in the fraction (the 2 in 1/2) would be
a million. The number of gluten parts would be the top of the fraction. A
further example, 20 ppm means that there are twenty parts of gluten per one
million parts of something else. Written in fraction form that would be
20/1,000,000. As you see, you are talking about very small amounts of gluten
when considering it in PPM. Let me know if this makes sense or if you get a
fantastic explanation that works better. Best wishes, Selena Eon 

Cecilia, TX

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