An Introduction to the Differences Between ASTM E74 and ISO 376, the Two Most Recognized Force Standards: The differences Between ASTM E74 and ISO 376 can be confusing. Morehouse has been performing both ASTM E74 and ISO 376 calibrations for more than fifteen years. We have been calibrating in accordance with the ASTM E74 standard since its introduction in 1974 and performing ISO 376 calibrations since sometime in early 2000. Until recently, we assumed that the rest of the world and the force community knew that the standards were completely different and that either standard could not be substituted for another. This paper explains those differences in more detail.