For the electronic part, you need a Arduino Nano, a ADS1115, an OLED (I2C, 128x64px, 0.96'), a buzzer, a push button and a switch on/off. The alimentation is provided by 3x1.5V battery. I have used some jack to connect the gaz sensor to the analyser. I use a commercial sensor R17/Oxygen, commonly used for the analysis of diving gaz. I have used a small breadboard to connect all devices to the Arduino Nano. I have fix all connections with a hot glue gun.
The software save the calibration into the EEPROM of the arduino as you could switch off the analyser between each measure. Another function is the control of the stability of the signal. When the signal is stable, a logo "OK" is writen on the display.