"A man with one clock always knows the time. A man with two or more is never sure."
This sums up the calibration issue for me. IIRC, most of the hi-end Sekonics(e.g., 508, 558, 608, 758)have a calibration function in 1/10 stop increments. I'm a little dubious about the Gossen on-board "zone" calibration feature--sounds nice but...The Sekonic target method seems vulnerable to error. Besides, I've got enough USB ports in my life already!