The f/16 RULE

[becca]

I am currently doing an assignment on the f/16 RULE. So far, the info i have is:

The rule states that if working in full sun, set the aperture to f/ 16 and the shutter speed will be equal to the reciprocal of the ISO. In practice, for example you are shooting at an ISO of 100 in full sun; simply set the aperture to f/ 16 and the shutter speed to the reciprocal of the ISO, which is 1/100 second.

You can of course use any combination of shutter speed and aperture as long as it converts back to f/ 16 at 1/100, such as f/8 at 1/400 or the like. This trick generally works quite well, but be mindful that if the scene is a bit shadowed then you must do a bit of interpretation and make some exposure adjustments

I sort of understand it but the maths gets me a bit muddled up! Does anyone have an easier way of explaining it? Would that mean that f/4, would be ISO 1600, taken at 1/1600 ?!!