I calibrated my Alco-Sensor with a .038 alcohol gas tank. Can I use a .082 gas tank to do an Accuracy Check, or must I use a .038 alcohol gas tank to do Accuracy Checks?

The short answer is yes.  One may use any alcohol gas tank to check the accuracy of an Alco-Sensor regardless of the alcohol tank used to calibrate the device.  

The reason is that Alco-Sensors are “linear” between the range of 0.000 and 0.400.  A device is linear if it gives results that are directly proportional to alcohol concentration.  

For example, a device reads accurately at .038. 

• If we then double the alcohol concentration of the gas (2 x .038 = .076), we expect the Alco-Sensor result to be .076. 
• If we triple the alcohol concentration of the gas (3 x .038 = .114), we expect the Alco-Sensor result to be .114. 
• If we halve the alcohol concentration of the gas (.038 / 2 = .019), we expect the Alco-Sensor result to be .019.  

If we plot these results they will form a straight line from .000 to .400.  Therefore, we know that if the Alco-Sensor reads accurately at any one point on the line between .000 and .400, it will read accurately at every other point on that line within that range. 

Linearity is established by the manufacturer through an extensive series of tests similar to the ones described above.  We rely on Intoximeter’s linearity testing to know that the Alco-Sensors are linear in the stated range.  Operators are not expected to perform their own linearity testing unless they operate in a laboratory or scientific setting.

Therefore, a user may perform Accuracy Checks with an alcohol gas tank of any alcohol concentration, without regard for the alcohol concentration of the tank used to calibrate the Alco-Sensor.  For example, if we document that the Alco-Sensor reads accurately at .038 using a .038 alcohol gas tank, we can be confident that the Alco-Sensor will give accurate readings at every other point between .000 and .400.