Hello all, thanks for taking a look at this guide.  We are in the business of buying and selling used electronic instrumentation.  Our clients include you folks on eBay as well as direct industry and other commercial contracts. 

Many times we are asked about calibration, if it is necessary and exactly what it means. 

First off, the primary standard for referring a calibration certificate is from the National Institute of Standards and Technology or NIST.  This is a government organization with accredits calibration laboratories.   If you see a seller who is selling a piece of equipment with a NIST Traceable calibration, make sure you ask them who their calibration laboratory is and then go the accredited laboratories web site and make sure that the lab is indeed registered.   Obviously, the lab must have test equipment that has a testing resolution higher than that of the equipment under test.  (For example, you wouldn't want a 5-digit multimeter calibrated with a 4-digit multimeter no matter how good and traceable the 4-digit meter is.)

The next thing of which you should be aware is what calibration standard is being applied.  There are manufacturer standards, DOT standards, ISO standards, DOD standards and so on.  Make sure you pick the one that is appropriate for you. 

The most critical thing to understand is that many labs which supply the label of calibrated are NOT paying to have an outside agency come in and verify their equipment or standards are up to snuff.  That is not to say that they are not doing a good job, but the fact remains that most of the calibration industry which operate outside of stricter standards (like ISO) do so without strict oversight.  So to you, the buyer, the term calibrated may have many different meanings to different labs.

Finally, do you really need a calibrated instrument?  Most manufacturer's of  scopes, signal generators, multimeters, etc. supply performance standards in their service manuals.  If a reputable dealer verifies that the instrument meets its performance standards then you can very likely get a very good deal on a piece of equipment and expect that the equipment will meet your requirements.   Obviously, some instrumentation is more critical than others.  A signal generator which has 1 Hz resolution at 1 MHz sounds good but do you need that level of performance?  An oscilloscope is primarily a visual instrument and, unless there are inherent counters, voltmeters, phase displays, etc built in, is limited to the resolution of your eye.

My honest opinion after working in engineering for over 30 years is that a full and traceable calibration is probably not necessary for the majority of equipment and applications.    Look at a seller's feedback, read their listings and ask questions.  Look at their return policy and even contact some of their buyers.  If things look good, they probably are and you will do fine.  If not, stay away.

Thanks for taking the time to review this guide.  If you have any comments, suggestions or experiences of your own, please write us at ERevisited@aol.com  and we will update this information.