Changes in ANSI standards regarding 0 dB HL

["Daniel E. Shub" <daniel.e.shub@xxxxxxxxx>]

I am feeling a bit over my head regarding the standard defining 0 dB
HL. I have a set of longitudinal audiograms collected from 2000
through 2015 in the US. The audiograms are reported in dB HL and were
measured according to the standard at the time and location of the
measurement.

>From what I can piece together, dB HL in the US is defined by ANSI
S3.6 (written in 1969 and revised in 1989, 1996, 2004, and 2010). Has
the relationship between dB HL and dB SPL (and maybe dB RETSPL)
changed since the introduction of ANSI 3.6? If so, were clinics
required to change to the newer standard on a particular date?