Whats the difference between hard and soft metric conversion?
The terms hard conversion and soft conversion refer to approaches you might take when converting an existing dimension from non-metric units to SI. “Hard” doesn’t refer to difficulty, but (essentially) whether hardware changes during the metrication process. However, the terms can be confusing and are probably best avoided, because they’re not always consistently defined and their meanings can be non-intuitive. It’s simplest to consider two cases, “converting” a physical object and conversions that don’t involve an object.
