Most Dissolve Oxygen sensors require one-point or two-point calibration. Before a one-point calibration can be carried out, the correct barometric pressure data must be fed into the sensor's meter. The two-point calibration runs in a zero-oxygen solution which is usually prepared by dissolving a zero-oxygen tablet in 40ml of pure or deionized water. The sensor's model number determines the kind of calibration it operates on and this information can be obtained on the product manual or by searching up the model number on a search engine online. A typical sensor is designed to fit into the flue of a gas or biogas boiler. It is also connected to a V25 version XY-LC interface board. This means that the voltage output is within 0 to 10 volts representing 25% oxygen. The sensors do not need a reference gas, meaning that there is absolutely no need to get a particular gas concentration to one side of the sensor. Everything is connected, and this makes such activity unnecessary.

Here are some guides to follow in the calibration of oxygen sensors:

To perform the calibration, the calibration input of the board is to be short-circuited to zero volts for a second or more. However, this depends on the type of sensor used. Some of them would require a manual short-circuit, others are done with a switch, while some have been digitally automated to do the short-circuiting on their own without any human operator needed. Some automated sensors also autocorrect according to the surrounding temperature which enables them to be operated in the laboratory (indoors) or on the field (outdoors).
Gas detectors that are equipped with electrochemical oxygen sensors of either one-point or two-point calibration should be set to 20.9% by volume in outside fresh air before indoor use or for other enclosed places. This function is frequently called "auto-set" or "zeroing" of the oxygen sensor and is really the process of using outside fresh air as a 20.9% by volume oxygen calibration gas standard (in atmospheres up to 14,000 ft. elevation).

The sensors do not require two-point calibration. Neither do they need to be on zero volts to offset calibration? They simply need a span calibration, which can be done with almost any kind of gas. The simplest way to do it is in the fresh air, and it measures oxygen.
Water calibrations are more capable of stabilizing temperature than air calibrations. They are therefore better used outdoors than indoors.
Operating the sensors require serious caution because they are extremely hot. Oxygen sensors are heated up to 700 Celsius (700â�°C). They are usually protected by an equipped porous cap whose temperature can reach up to 250 Celsius (700â�°C). It must not be touched.
The calibration gas cylinder usually indicates a date of preparation and a recommended expiration date. Usually, Product manuals include the procedures for calibration operations in a maintenance section of the manual. This may indicate one or more oxygen gas bottles of different concentrations are necessary to set a "calibration window" for the device.
It is possible in some oxygen monitoring instruments such as the ENMET AM-5175, ISA-40, ISA-42M, ISA-50M, and ISA-60M to use the surrounding air in which the sensor is located to set the oxygen reading to 20.9%, which should appear on the LCD display of the device.

You can find more information on how to calibrate a medical oxygen sensor here.