Hi,
Still that device is handy to check that during the season a tree doesn't get shaded by rabbit-growing trees .
I had to cut back my peach trees last year as they were shading some fig trees and the garden. I was thinking it was the garden house but when moving the branches of the peach trees, I saw they were culprit - and my blackberry bush as well.
I removed half of the canes of the bb this year due to the observation I mad last year. This is sad and good, as normally, the remaining bb fruiting branches should put bigger fruits *hopefully* .