14KP is 14 karat plumb/pure. It's 14 karat (.585) purity gold. The JTL is an artist's (or owners, less likely) initials. Normally 14 karat could be used to describe something with something like 2.2% less gold purity.
Jack the Lad goes by JTL.
firstly check calibration dates, PAT testing and give the tool a visual check to ensure it is in good physical state to use. if it has a a test procedure, this should be followed accordingly. (^rough answer - jtl might not accept it lol)