Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Precise nature


On their data sheets for geotechnical instrumentation, some manufacturers give a number for resolution, but nothing for accuracy or repeatability.

I don't find this useful. It can be misleading if a user is unsure of the meaning of the terms, and believes that this number refers to accuracy or precision.

Resolution is the smallest division on the instrument readout scale.Accuracy is the closeness of approach of a measurement to the true value of the quantity measured.

Precision (a synonym for repeatability) is the closeness of approach of each of a number of similar measurements to the arithmetic mean.

As a user, I need to know either accuracy or precision. I need to know about accuracy when I'm interested in an absolute measurement, such as when measuring pore water pressure or total stress.

I need to know about precision when I'm interested in a measurement of change, such as when measuring deformation (I don't care about actual position in this case, only about change of actual position).Do I care about resolution? I don't think so - it seems to me that this is one of the issues that a manufacturer needs to address in system design, in order to arrive at the stated accuracy or precision.

If this is correct, please tell us about accuracy or precision, and keep the resolution issue to yourselves. If you have a different view, please share it with me.

On a similar subject, I recently found that an instrument didn't live up to the manufacturer's stated accuracy.We discussed it.The manufacturer offered, in subsequent publicity, to 'reset user expectations'.

I thought that was a masterpiece of gobbledegook.

John Dunnicliff, geotechnical instrumentation consultant, Devon

This letter is an extract from the September 2000 issue of John Dunnicliff 's regular Geotechnical Instrumentation News (GIN) column written for Geotechnical News, and is used here with the kind permission of BiTech Publications, Richmond, British Columbia, Canada.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.