On 21/02/2017 17:19, Nick Maclaren wrote:
You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

You're missing the point. Unlike a floor in a house a garden isn't a
flat plane. Which means that one leg of a 4 legged ladder is always off
the ground.

And that means it is _less_ stable than a properly designed three legged
one, as it rocks between the two stable configurations...

I have a step ladder with bars across the base of each step. It's great
indoors. Outdoors I have to fiddle around for ages so it doesn't rock,
sometime putting bricks under it

Andy