In the past, Unifiber reported the measurements for masts from other brands using pre-defined categories (hard top, soft top, constant curve). They have now changed that to instead show which of their three mast types fits other brands best.
They explain the rationale for the new classification system at
unifiber.net/windsurf-masts/bend-curves quite nicely. Basically, all brands now use a relatively narrow range in the "hard top - constant curve - soft top" spectrum. None of the major brands still use hard top, virtually all brands use either constant curve or soft top. But within the soft top range, there are significant differences in how stiff the center of the mast is. The "FL" and "FH" masts are both flex top, but FL has a more flexible middle section, while FH has a harder middle section.
When the "hard top - soft top" classification was developed last century, the differences in bend spectrum were huge, with number from 0-6 for hard top to 22+ for "super flex top" (numbers are explained at
boards.co.uk/features/masts-what-does-it-all-mean.html). Back then, the "hard - constant - soft" classification was quite useful. But now, masts are all in the 10-17 range, and a finer description makes sense.
The top hardness numbers are based on three measurements, the deflection at the center, 1/4, and 3/4th of the mast length. It assumes that center deflection is the same for a given length (which supposedly is large true, since masts of a given length tend to have the same ICMS number). But in the ends, the three numbers are mingled together into just one number, which means some information is lost.
Ezzy is one of the few brands that actually states both 1/4 and 3/4 deflection numbers for the masts that work with their sails. Most other brands do not, since they'd rather have you buy their masts. Unifiber also gives the top and bottom numbers for their three mast types. Interestingly, all three types match the ranges given for Ezzy sails, although the FH mast is at the edge of the Ezzy ranges, and therefore probably the worst choice of the three kinds. If other sail and mast brands would also just publish the 1/4 and 3/4 deflection numbers for the masts that the sails were designed for, things would be much simpler.