Adjusted barometer for sea level reading

I did it roughly when first installed, but am now comparing it to Kenley and Biggin Hill and it seems a tad low. I've inched it up by 1hPa, giving a total now of 9hPa above the unajusted reading from the indoor sensor. I think it should go up another one, but I'll leave it a month and then check it with the MADIS analysis presented by Philip Gladstone.