Fuel Economy - What do you get out of a tank? (3rd gens only)

[Galois]

I just replaced my 02 sensor, I drove to the workshop and the readout was 13.8 l/100 average, fitted the sensor and got 10.5 l/100 on the same return trip in more traffic.

Damn I'm doing that then. I got 15L/100km on the first tank, given I had a bit of novelty driving and I came from driving an r34 gtt skyline, but I was still pretty shocked. Need to tame my right foot I think

[SH00T]

I only did this after knowing eberything else, about my car, leads, plugs, air filters, servicehistory, etc
And I have seem a gradual decline in economy.
At 150 a pop, I'd check it out with a multimeter beforehand.