An Inaccurate Gauge: The Impact of Measurement

Kati Anglin - Human Factors Engineer

"Well, it looks like I'll be Flinstoning my way back home," I mutter to myself as I fill with regret for not stopping at the gas station. Given that my car still runs well below "E,"  I like to gamble on the accuracy of my fuel gauge.  Luckily, I not only made it back to my house, but I also made it back to a gas station. This isn't an uncommon occurrence. I have seen my fuel gauge indicate that my tank is empty, yet my car runs at least 30 miles further. This is due to the design of the fuel tank.

​Here is a brief description of how most cars detect the amount of gas is in the tank. Cars use a "sending unit," which consists of a float attached to a long, metal rod that is then attached to a resistor. The resistor attaches to a spot in the fuel tank, with the float bobbing on top of the gas. As the gas goes up, so does the float. Without explaining too much about the resistor, the float takes part in changing the signal sent to the car’s computer, which tells the driver how much gas they have. As the tank empties, the float nears the bottom of the tank. However, the float can't reach the bottom of the tank where there is still fuel, so it thinks the tank is empty. This is why, in most cars, the needle goes below empty and eventually stops moving while there is still gas left in the tank.

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Although the fuel gauge is intended to provide input to the driver and prompt action, the inaccuracy has created a habit of risk-taking when my gas tank runs below “E.” As I approach my destination, I am less likely to pull over to get gas because I can "probably" make it. While the fuel gauge is an inconspicuous example, an inaccurate gauge can result in people not taking it seriously and, even worse, breed bad behavior.

My inaccurate fuel gauge made me reflect on other important "gauges" in most people's lives, such as measures in the workplace. Measurements are intended to provide insight into individual and organizational performance; however, they can be unintentionally distorted and, in turn, made inaccurate (i.e., invalid). For example, an instructor's effectiveness is evaluated based on how many students they pass, so they push through a failing trainee. An automotive employee receives bonuses by meeting production quotas, so they produce cars quickly without being concerned with quality standards. The organization that employs the instructor doesn't want failing trainees to pass, and the automotive company doesn't want low-quality and unsafe cars. However, they both are supporting the wrong behavior due to their methods of measurement. They are not accurately measuring the intended behaviors, which makes the measurements dangerous. 

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Before implementing a measure that seems to be a good idea, ask yourself and others the following questions:

Does the measure actually reflect and capture the intended focus?
If your goal is to measure weight, you should be using a scale instead of a ruler. This example (albeit oversimplified) depicts the validity of a measure. Validity has the power to make the data useful, while that lack of validity becomes dangerous and supporting the wrong efforts.

Are you using the right metrics?
If you are measuring anything, you should be able to compare it to something (e.g., past performance, competitor performance; research). However, there should be a reason for these metrics. Pulling numbers out of the sky will either lead to people finding ways to cheat the system (if it's unattainable) or not take the measure seriously (if it is easily attainable).

How can you use the results? 
Based on the data you collected through measures, what guidance or actions can  you take to improve the situation? Frequently, organizations measure performance without actually doing anything with it. This leaves the measurement a waste of time and money. If you are wanting to measure performance, plan for a remediation strategy

When have you seen an inaccurate measure create unintended behaviors? Let us know.

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