Due to the remarkably consistent properties of Extra-Virgin Olive Oil, one drop of it on the slide will always read between 71 and 72 on the Brix scale. If you set the lock-nut to show any such oil at 71.5, you will have correctly calibrated the water content scale at the same time.
Sunflower oil (Sainsbury’s) 25.0%
Olive oil regular (Sainsbury’s) 27.2%
Olive oil regular (Bertolli) 27.2%
Olive oil, Spanish extra virgin (Sainsbury’s) 27.0%
Olive oil, Italian extra virgin (Filippo Berio) 27.0%