Have you ever looked at a product with specifications that seem too good to be true? As it turns out, you may be right. Far too many product specifications are carefully worded to sell units instead of basing their specs on sound, scientific practice. Depending on how a manufacturer decides to test their product, they may publish numbers that are misleading at best and meaningless at worst. Keep an eye out for these tricks and you won't end up purchasing an instrument that doesn’t fit your needs.
Specification Validity Over TimeProducts with specifications that fail to report a period of validity may be ignoring drift that happens over time. A freshly calibrated instrument could be accurate the day it arrives, but you should be confident in its accuracy in between calibrations. Ensure that the specifications listed are guaranteed for a full year and not just upon calibration.
The word "typical" can sound reassuring, but the term has a variety of meanings on a product data sheet. For most manufacturers, “typical” describes a specification that has been thoroughly characterized but is not verified on every product. For others, the term can be used to avoid accountability for unsubstantiated claims. Be wary if the specifications are only described as typical without any mention of confidence levels or value distribution.
It’s natural to try and generate sales by highlighting the best features of an instrument. Where we get into trouble is when one specific feature overshadows the integrity of the overall system. To illustrate this, consider that some foods are branded as "low fat" to give the impression of being good for you, leaving the high sugar content information buried in the nutritional information fine print. This example at least makes the additional information available, due to food industry regulations. Other industries are free from these regulations: manufacturers may include whichever specifications they choose. This makes it much more difficult for users to identify specification holes.
The best strategy to avoid this trap is to look at specification lists from multiple companies. If a specification is listed with one manufacturer and not another, there’s a good chance that this unlisted parameter either hasn’t been tested, i.e., the performance is unknown, or it has intentionally been excluded from publication.
Narrow Operating Conditions
When accuracy is specified for a very particular temperature — or when the specs fail to mention temperature at all — be sure to check the temperature coefficient specifications. Small changes in temperature may result in large changes in accuracy, so make sure to purchase a product designed to perform properly under your specific environmental conditions.
Even products that use proper statistical methods may only specify one standard deviation of the distribution. In this case, one in three products will fail to meet the specification. It is considered best practice to use at least two standard deviations for 95% confidence or better.
When profits take precedence over transparency, the consumer pays the price. Next time you’re in the market for a magnetic instrument, take a critical look at the product specifications to ensure that it’s the right choice for your application.
Not only is it important to choose the right instrument, knowing how to use it helps you obtain accurate data. Download the white paper on Common Sources of Error in Magnetic Measurement.