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I get stumped on stuff like that all the time. Thank goodness for the internet!
Most agree that the expected legal range for the field strength limit of 250 uV/M is going to be around 200 feet on an average receiver.
One way to look at that is to see the transmitter in the center of a circle with a 200 foot radius
Area of a circle = pi X radius squared
3.14159 X (200 X 200) = 125,663.7 square feet
For reference, square mile = 5,280 X 5,280 = 27,878,400 square feet
Square root of 25,000 = 158, so the manufacturer has either put the transmitter in the center of a square 158 feet on a side or if in the center of a circle:
3.14159 X something squared = 25,000
25,000/3.14159 = 7957.75
Square root of 7957.75 = 89.2
So with a circle with a radius of around 90 feet, not 200, the manufacturer in this case seems to be within accepted part 15 limits, but I agree, at first glance, a range of 25,000 square feet sounds way out of line.
Great marketing ploy 🙂