Unfortunately, there is no simple answer to this.
Whether or not you need a calibration certificate is dictated by the guidelines/legislation of the industry you are working within. As a general rule, if you are working within the food industry or in laboratory type applications, it is highly likely that you will need a calibration certificate with your thermometer and that this will need to be renewed at least annually.
On the other hand, if you are using your instrument as a rough check during a non-critical mechanical or industrial application, a calibration certificate may not be necessary.
If you need a calibration certificate, please ensure that you mention this when discussing with Eurolec - some of our range are provided with a certificate as standard e.g. models PC Temp PT2 and Testo 106-T1.