Dissolved Oxygen Sensor (Mountain View nr train station)

This is for measuring the amount of dissolved oxygen in a pond or aquarium.
It is new, never used, but was purchased a little less than 2 years ago.
I should point out that after reading the instructions and reviews on Amazon, it is a little complicated to use, as there are various calibration steps you must perform each time.
Also the box is is slightly soiled on the outside but everything inside is pristine.