“…Again, the dominant effect of errors in EHT, rate, years are taken as nominal, as is an EHT uncertainty of SIGEHT ¼ 1 C (Rogers, 2007(Rogers, , 2008a. Water and rate variability have only been measured for Coso obsidian, which may not be typical; however, obsidians from the Coso field exhibit rate coefficient of variability between w0.07 and w0.5 (Rogers, 2008b;Stevenson et al, 1993), so a nominal value of CVK ¼ 0.2 was chosen for analysis. Age variability due to site formation is more difficult to quantify, but a value of CVT ¼ 20% of age seems reasonable.…”