The Advanced Reactivity Measurement Facilities, ARMF-I and ARMF-II, were nearly identical critical facilities and were used almost exclusively for measuring reactor physics parameters, such as reactor-spectrum cross sections and resonance integral cross sections. They were designed to (a) have large statistical weights for fuels and poisons, (b) be mechanically stable enough to produce reproducible reactivity measurements, and (c) have sensitive instrumentation capable of measuring very small reactivities.