This is a question we are frequently asked. All our scopes are tested after production and are guaranteed to meet the published specification for that scope. In normal use your 4424 will not drift out of it's published specification. Certain measurement applications require the use of calibrated test equipment for legal and safety reasons and we can provide a Calibration Certificate for the 4424 but that does require that the scope is returned to us for calibration and there is a fee for this (£60 + carriage + VAT). We recommend that the certificate is renewed yearly. If a calibration certificate is requested from new, or a scope is later returned for calibration, the actual errors & accuracy for that particular scope are measured and recorded on the certificate. For example, a scope might have a published accuracy of +/-3% for voltage. An un-calibrated scope will meet or better that accuracy. A calibrated scope will have the actual error recorded for each voltage range and that error might be a reading that is 1% high. This error can now be allowed for when taking accurate measurements. There are certain tasks where it is obligatory to use calibrated equipment, for safety or regulatory reasons. For normal laboratory use, where the readings are for monitoring and fault-finding purposes only, calibration is not required.
A scope measures voltage & time, only the voltage is calibrated, the time is crystal controlled and more accurate than any reading that can be resolved on the screen.