Can you tell me what is the average precipitation at the Amersham station?
SELECT avg ( t1.precipitation )  FROM weekly_weather AS t1 JOIN station AS t2 ON t1.station_id  =  t2.id WHERE t2.network_name  =  "Amersham"
average precipitation = AVG(precipitation); at the Amersham station refers to WHERE network_name = 'Amersham';