A Biological Indicator Evaluation Resistometer or BIER vessel is a piece of equipment used to determine the time taken to reduce a bioload by 90% (also known as a log 1 reduction). The name derives from how the equipment is used. A BIER vessel evaluates the resistance of biological indicators to moist heat (steam) sterilization. For example, if a 90% reduction is determined to be 5 minutes for the microorganism being evaluated, then a D-value of 5 is assigned. D values are specific to starting bioload, substrate (the material the spores are on) and microbe species. BIER vessels typically cost in excess of $100 000US and therefore tend to be located where biological indicators are manufactured.