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Bruce Hamilton

Six Sigma

Insignificant Digits

Are you stepping over a dollar to save a dime?

Published: Tuesday, July 12, 2011 - 16:03

Significant digits, the number of digits to the right of a decimal point that are warranted by the accuracy of the means of measurement, are a critical part of scientific investigation. In developing products and services, the concept is essential. For example, how many products have failed to “delight” customers because of tolerance stack-ups on component parts? And how many of those components have failed to meet spec because the significant digits of the design did not match the capability of the production process? In these cases, the number of places to the right of the decimal point is very significant.

But in many cases, the accuracy of our measures is insignificant. Take, for example, the price of gas at the pump. Why not $3.80 per gallon instead of the mixed decimal and fraction rendering we usually see? The answer is that during the 1930s when gas price was 10–9/10 cents per gallon (equal to about $1.40 per gallon today), a penny was worth 10 percent of the price of the gallon—pretty significant. The fractional price derived from an attempt by retailers to minimize the cost at a time of gross oversupply. Today the condition is reversed; the third decimal place (the 9/10 as it is usually shown), and arguably even the second, is not significant at all, at least not in a practical sense.

So it is with allocation accounting, another measurement system mostly developed during the Great Depression. According to management accounting expert Brian Maskell, “the bulk of current accounting methods formalized in the 1930s has changed very little since.” A highly subjective cost-accounting allocation scheme, for example, spread “insignificant” amounts of 1930s overhead over labor cost. Even then it was at best a rough approximation intended to recover the cost of nonproduction resources. Today that once-insignificant figure amounts to a gigantic lever on relatively small labor amounts.

Overhead multipliers (O), once just small fractions of labor (L) and even material (M) costs, are often two to three times the cost of labor today. Call this an unintended consequence of the second industrial revolution. In the words of Eli Goldratt, “traditional cost accounting is ‘precisely wrong.’” However significant the number of decimal points on a labor time may be from a scientific context, they are worse than insignificant in the bigger picture. Yet many organizations continue to scrutinize value-added functions to four decimal places while ignoring huge nonvalue-added wastes. Make vs. buy and pricing decisions based only on this model are as relevant as the 9/10¢ at the gas pump. The difference is that gas pump prices, while confusing, are essentially harmless, while traditional management accounting decisions are killing American business.


About The Author

Bruce Hamilton’s picture

Bruce Hamilton

Bruce Hamilton, president of the Greater Boston Manufacturing Partnership (GBMP), brings hands-on experience as a manager, teacher, and change agent. Prior to GBMP, Hamilton led efforts to transform United Electric Controls Co.’s production from a traditional batch factory to a single-piece-flow environment that has become an international showcase. Hamilton has spoken internationally on lean manufacturing, employee involvement, continuous improvement, and implementing change; and he has contributed to numerous texts ranging from visual control to variety reduction. Hamilton’s blog, Old Lean Dude, is an on-going reflection on lean philosophy and practices with an emphasis on keeping good jobs close to home.