WHAT IS PROCESS TOLERANCE?
Whether it’s the weight of an ingredient or the thickness of paint, no two products are exactly the same. These differences are not only caused by measurement uncertainty, they are also caused by tolerance built into the procedure. Process tolerance is part of an age-old struggle between product quality and costs. In the simplest terms, tolerance can represent “good enough.” The phrase “good enough” may send chills down your spine and make you retort, “Only perfection is good enough,” but the use of tolerance is absolutely necessary. You’ll never see it in a marketing campaign, but even high-quality luxury brands utilize this “good enough” factor in virtually every step of their process.
In practice, Process Tolerance defines the minimum and maximum standard deviation allowed in the production of goods. This deviation is generally represented by a +/- value following a reference amount. For example, the procedure to make a sauce may call for 10.0(+/- 0.5) oz of basil. This means the end products can have between 9.5 and 10.5 oz and still be considered in tolerance. It’s worth noting that it does not need to be an even split. A tolerance could have different upper and lower limits such as 10.0(+0.2 -0.5) oz.
WHY IS IT IMPORTANT?
Don’t be fooled. Tolerance is not a symptom of being cheap or lazy; it is the exact opposite. Since consistently hitting a desired target exactly is impossible, an acceptable guideline must be established to ensure quality and safety. Generally, a tighter tolerance will increase quality while making the process exponentially slower, more expensive, and increase the potential for waste. These costs can greatly impact the success of a company and the costs to consumers.
HOW TO DETERMINE YOUR PROCESS TOLERANCE
When determining a process tolerance, the goal is to balance product quality/consistency with production costs. This is normally achieved by combining Worst-Case Tolerance, Statistical Tolerance, and other unique factors for your process into the same analysis.