Have you calibrated the meter? You need at least two standards and calibrate the range for the standards you have.
Rinse the probe well and dip in 4, for example. Turn the appropriate pot gently until you are on 4.00 for 4 then do 10 or 7 same way. Do this 3 or 4 times.
I've had one for years and even left the probe uncapped during a hiatus.

Best bet for storage is a 7.45g of potassium chloride into 100ml of water.

If you have had any water in the unit I'd open it and put it in the refrigerator for a day.
I will agree the 16.6 reading is odd and does not give a warm and fuzzy feeling.
Nice meters but as you said a bit salty.