Distance formula?

Hi everyone,

I'm trying to find a formula I once had to help with calculating my distance from shore. It went something like:

If you can see land you are 5 miles off, If you can see the shore you are 1 mile off, If you can see people you are 800yards off, if you can see the arms and legs you are 500yards off, If you can see their faces you are 200 yards off, if you can see their features you are 80 yards off, and so on.

My figures are probably incorrect but it is a great quick reference guide, particularly if you are giving your position to anyone, and you don't have the benefit of GPS, three way fixes or chart plotter to hand.

Has anyone heard of this formula or know of any links to sites that have similar?

Thanks

Simon 

If you cannot see the leeward bow; you way be in trouble

If you cannot see the windward bow, you might be in trouble

If you cannot see the front beam, you are probably in trouble

If you cannot see the Spi pole, you are almost certainly in trouble

If you see the back beam it may be to late.

they saved this one:

If you can see the front of the boat and you are wet; it’s too late….

Don't listen to them, if you can see the baddies you're way too close...run away call the paras or get an airstrike.