Natural Uranium Ore COFFINITE Weight: 7.7 oz. Radiation: 23,200. CPM (counts-per-minute) $21.00 plus $12.80 shipping This rock was collected during July 2025 at Jurassic Canyon, 18 miles NW of Grants NM. This rock has TWO WHITE DOTS, which identify the two surface locations with the strongest response of radioactivity. ACCURACY OF MEASURED RADIOACTIVITY LEVELS Every rock has a radiation number labeled on top of the metal foil wrapper. My own measurements are HIGHLY ACCURATE. Each measurement has been done with a LUDLUM 2200 GEIGER-SCALER. This is the most accurate radiation measuring device available to hobbyists like you and me. I have THREE Ludlum 2200 geiger-scalers; two are shown in the attached photos, and a third was purchased as a spare. One was calibrated by geiger expert Tom Hall (RADINC; based at Stewart, Florida); I adjusted the other two. They are highly accurate because a geiger- scaler instrument actually counts every tick, then shows the count-total on a six-digit digital screen, as you view on the attached color photos. DO A "CAVEMAN CALIBRATION" ON YOUR OWN GEIGER "Its so easy, even a caveman could do it." Here's how: Every rock I ship to buyers has a label on it, showing the measured CPM geiger response. Remove the metal foil, then measure the white dot on each rock. If YOUR MEASUREMENT differs from the number on my label for that rock, then ADJUST THE RANGE-LEVELS on your own geiger. Every Ludlum, Bicron, or other classic geiger has three or four range-adjuster potentiometers. For each measured rock, choose the range- adjuster that has the labeled value in the center of its displayed range on the meter. If you can get your measured radiation value very close to the value written on the gummed label that came with the purchased rock, then your instrument has had a "caveman calibration." I round the measured values to the nearest 500 cpm value, which is accuracy within 5%. On the web, the biggest "geiger calibration rip-off" is a vendor ad that solicits a calibration service on the yellow civil-defense geigers from the 1960 cold war, for those CDV-700 units. In the ad, the vendor offers a calibration service for about $90.00 when the geiger is mailed. Yet, the printed owners manual for the CDV-700 civil defense geiger has A SINGLE PARAGRAPH that instructs the user how to use the attached "cesium check source" on the right side of the metal case to do a simple calibration, merely by adjusting a single potentiometer, located on the geiger's internal circuit board. I will happily send a photocopy of that self-calibration paragraph; just mention that you want the photocopied self-calibration for the CDV-700, when you buy a uranium rock from me. It will then be enclosed with the purchased rock being mailed. Stephen Buggie, Ph.D. "Have geigers, will travel." Professor Emeritus Univ. of New Mexico, Gallup