I suspect 60 feet is a bit wide (or high!) of the mark. I've found 2 photos of the platforms showing 5 levels, not 9 as mentioned somewhere else.
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Description: Photo 1Description: Photo 2
The first clearly shows 12 steps and, at say 9 inches each, makes the distance from board 4 to board 5 about 3 metres. Scaling the heights of other boards from an estimated water level agrees with the above text figures of 10 and 3 metres. The heights of the person sitting at the bottom of the tower and the children to the right just about confirm my calculations.
Photo 2 is less clear but, using the 12 steps again, there is a person on board 5 who scales about right.
'Seven' metres sounds unusual and it's surprising that metres are used at all, bearing in mind that the pool, 100 metres long, was built in 1934, when we had an Empire and used yards, feet and inches, etc., elsewhere! Presumably the metric measurements, also in athletics, came from the Olympic Games.