In 1962 John Rollet published a paper in the IRE called Stability and Power – Gain invariants of Linear two ports. In this he described the K – factor for an amplifier. When designing an amplifier or selecting one from a catalog, check the K factor. If the K – factor is greater than 1, then the amplifier is unconditionally stable, if not then it should be checked for stability. It could be conditionally stable, or in the worst case, unstable. You can access a javascript calculator from the Signal Processing Group Inc,. website to calculate K. Just select the complementary menu item and choose the calculator link,