Here’s how I interpret this chart:
In the past there was conventional wisdom that generically stated that damage to blossoms was likely to occur at a certain temp for each type of fruit tree. This is referred to as the “Old Temp.” It was probably an educated guess that erred on the side of caution. They’ve since ran more tests and came up with some better educated guesses. They’ve also given a range showing when a little damage happens and when a lot of damage happens. 10% represents the temp at which you can expect 10% of the buds to be killed which is probably no big deal. 90% represents the temp at which 90% of the buds will be killed, which is a much bigger deal, but for a backyard grower can still mean getting a handful of fruit.