Share 'Calibration of Babolat Star stringer.'

I own an old Babolat Star stringer. Circa 1985? I often check the racquet tension after stringing with the STRINGMETER mk VI by Polycraft. I'm thinking the calibration may be off. Should I invest in a calibrating device for the stringer? And if so. How do I calibrate it? The stringer's been running like a champ, but it's nearly 15 years old and how accurate is my tension? This is what my stringer…