Patti James, a 28th Medical Support Squadron medical laboratory technologist, loads control specimens into a medical centrifuge at Ellsworth Air Force Base, S.D., Dec. 4, 2018. After a control group has been tested, technicians use a previously tested specimen from earlier that week to cross-check the validity of the results. (U.S. Air Force photo by Airman 1st Class Nicolas Z. Erwin)