TESTS on modern aircraft have shown that a small advantage is to be gained by the use of pendulum stabilization over the spirit level, but it is hardly considered sufficient to warrant the additional complexity of mechanism involved, particularly when it is effected in the clumsy manner of this design. The pendulum and sighting assemblies weighs 20 lb., and the base and supporting arm 14 lb. in all a total of 34 lb.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Oct 1, 1942