The theory is that bikes (when perfectly vertical) do not have enough surface area of metal over the coils to trigger them.

In still air, with the flame perfectly vertical, they begin to flicker.

This Copernicus was merely a deep shaft or well, with perfectly vertical sides.

Rolls-Royce is famous for arranging its grille bars by hand to ensure that they appear perfectly vertical.

And there it was: the perfectly vertical slash.

Genuine woodworm holes, on the other hand, would be of varying diameter and usually not perfectly vertical.

It stood up neatly, its arched handles perfectly vertical.

The back was a simple armoured box; the front plate was high and perfectly vertical.

However, a bullet fired at an angle not perfectly vertical will retain its spin on the way down and can attain much more lethal speeds.

Door frames are seldom exactly true - perfectly vertical and horizontal - so determine the average height and width.