Calibration is the act of adjusting or checking an instrument against a known standard that is more accurate than the instrument being adjusted/checked. Certification is the paperwork trail created by the line of traceable standards used to calibrated the standards being used to calibrate the instrument under test. Calibration is nice to do every once in a while for hobby purposes just to make sure that your instrument in question is still working OK. Sometimes, if we depend upon a certain instrument exclusively, we can end up not noticing that something's not right and will go nuts trying to make simple adjustments using an instrument that is horribly out of cal. For calibration labs and instrument manufacturers (e.g, Tektronix, Agilent, Gould, etc.), certification (traceablity) is an absolute must, especially if you're dealing with companies aligning to ISO or other standards. Calibration/certification with before-and-after test data is a RPIA for any technician doing the work. There's really no sense in a paper trail of statistical data just to look at the trends on an instrument. Who cares? If it's bad, fix it, don't write a history report!