I want to calibrate a barometer using current pressure. I live in a town with altitude 540m (at the top of an escarpment) but the closest internet pressure readings are from a town which is 50m above sea level(at the bottom of the escarpment). Assuming the temperature varies linearly between the two altitudes, and the atmosphere decreases exponentially, what rule of thumb can I use to convert a pressure reading from the lower town to my upper town? (This isn't actually a homework questions! : )

Question

I want to calibrate a barometer using current pressure.  I live in a town with altitude 540m (at the top of an escarpment) but the closest internet pressure readings are from a town which is 50m above  sea level(at the bottom of the escarpment).  Assuming the temperature varies linearly between the two altitudes, and the atmosphere decreases exponentially, what rule of thumb can I use to convert a pressure reading from the lower town to my upper town?  (This isn't actually a homework questions! : )