The standard method for measuring and correcting for extinction by the Earth's atmosphere is well known. However it requires 'photometric' conditions, i.e. the extinction must be constant across the entire sky and for the whole night. Due to our maritime climate, these conditions are very rare in New Zealand (and I expect it is similar in Australia but the audience is sure to tell me if I'm wrong). Approximately 30 years ago, the Vilnius Observatory developed another, little known, method for measuring and correcting extinction that can cope better with less that photometric conditions. This presentation will describe this method, which I hope will allow us to reduce the systematic error in our results that comes from applying incorrect extinction coefficients.