Throw distance definition



I am trying to figure out how to get the image size for a projector for a given throw distance. The problem I have is finding a definition of what throw distance is.

Some web sites state that it is the ratio of throw distance against the image diagonal

Other web sites state that the throw ratio is the throw distance against the width of the image.

What is the correct answer?

Also, if you look at the specification for an InFocus LP530

Min Throw distance: 1.5m
Throw Ratio 1.2:1

The table of projection distance /image sizes states that a throw of 1.5m will give a maximum image diagonal of 1.1m and a minimum image diagonal of 0.9m.

Using the equation

Diagonal = distance /throw ration

Gives us a diagonal of 1.25.

How do they calculate their figures?

Thanks in advance

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