Few hours drive from Bangkok, Thailand, there is a unique wet market known as "train market". The market is assembled very-very close & on the the town's railway track near the Ratyatraksa road.
Whenever, the train arrives, the stall owners, swiftly pull their stall's shades and re-position once the train passes-by.
Interestingly their naked eye measurement in setting-up the stalls, product displays and shades are practical to handle and precise enough for the train pass-thru without hitting any of the stalls or their products. It looks impossible but it has been their life routines, they have a very good way in maintaining the "measurement uncertainty", everything is done manually without any automation, sensors or measuring tape, but it works.
Measurement is common in our daily life even at kitchen while perfecting recipes. For laboratory, quality of a measurement depends on the capability to perform the measurement at high level of accuracy. Whereby accuracy is dependent on the precision and trueness.
Whenever, the train arrives, the stall owners, swiftly pull their stall's shades and re-position once the train passes-by.
Interestingly their naked eye measurement in setting-up the stalls, product displays and shades are practical to handle and precise enough for the train pass-thru without hitting any of the stalls or their products. It looks impossible but it has been their life routines, they have a very good way in maintaining the "measurement uncertainty", everything is done manually without any automation, sensors or measuring tape, but it works.
When an instrument, e.g. weighing scale displays same value of readings in a series of repeated weighing of the same item, it is considered to be very precise. While trueness is reflected by the capability of the weighing scale to display correct value of weight, which is predetermined by means of calibration using standardized weights, also known as "standard stone". Normally, an equipment calibration service will cover both precision and trueness, often represented by the value named "uncertainty of measurement" stated on the calibration certificate.
Definitely, an accurate measurement is a must but the level of accuracy must fits the purpose of measurement. There is tendency for some customers, auditors and laboratory managers to over-emphasize the accuracy level by increasing the readability (e.g. the number of decimals). Without realizing it defeats the cost-effectiveness, which is the ground rule of organizational survival.
Increasing readability does not necessarily increase accuracy. Let's compare a digital contact thermometer (CT) of 0.5°C readability that costs MYR50 to a digital infra-red thermometer (IRT) of 0.01°C readability that costs MYR500. Both will incur the same fee for calibration services, around MYR120. After calibration for use between 40 to 150°C, both are used to verify temperature of a stainless steel water bath being setup at 50°C, the CT displays 50.5°C and IRT displays 51.02 °C, which one is the best measurement? Knowing the control knob on the water bath shows increment of setting at 1 °C, does the water bath operation require accuracy of ±
0.01 °C or ± 1 °C is adequate for it's temperature setting? Perhaps it is more convenient with style to use the IRT, but do double check the user manual, don't be surprised to read that some IRT not intended for measuring temperature of metallic surface.
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