It refers to... 07:54 Apr 16, 2018
...a kind of tripod like an artists's easel, where the legs are not symmetrically articualted in a triangle (as for a photographic tripod), but the two 'front' legs only move out and in, while remaining in the same vertical plane as the main upright, and the 'back' leg only moves forwards and backwards, while reamining in the same vertical plane in the sideways direction. This requires a simpler and often sturdier hinge mechanism, but can lead to unequal forces, and the centre column may or may not be truly vertical.
That is in fact an over simplification! There are of course very many different types of easel, hinged in various different ways! Some have front legs that are not articulated at all, and just a back leg for adjusting the tilt. the key feature really is that the three legs are not all equally mobile in the same directions. |