Verkar så enligt wiki "One part per thousand should generally be spelled out in full and not as "ppt" (which is usually understood to represent "parts per trillion")" och per trillion är nog väldigt hög upplösning...kan det verkligen stämma isf: One part per trillion (ppt) denotes one part per 1,000,000,000,000 parts, one part in 1012, and a value of 1 × 10−12. This is equivalent to one drop of water diluted into 20 Olympic-size swimming pools (50,000 m3), or about three seconds out of every hundred thousand years.