I want to know the answer to the following question:
What eliminated comparability?
All the background I'm provided with is that "The system was later extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist Josef Maria Eder (1855–1944) and Flemish-born botanist Walter Hecht (de) (1896–1960), (who, in 1919/1920, jointly developed their Eder–Hecht neutral wedge sensitometer measuring emulsion speeds in Eder–Hecht grades).". Is that enough to answer the question?
Answer: no