On Thu, Jul 5, 2012 at 1:16 PM, Kevin Chadwick <ma1l1ists@yahoo.co.uk> wrote:
"[...] I'll simply state that 12 PPM correspond to one second per day roughly.
I'm skeptical and am more inclined to think ntp has measurement problems or a decimal has been missed or something but it's easy to check with real world direct simple data which I always prefer, so we shall see.
that value [12ppm] is correct -- `ppm` is a dimensionless ratio between 0 and 1; units *must* cancel, leaving only a pure coefficient which is then scaled to X/1,000,000 by multiplying by some N/N scaling factor. since there are 86400 seconds in one day, expressing a 1 second loss per day is the same as saying a 1 second loss per 86400 seconds, or: 0.0000115 = 1/86400 0.0000115 = 1/86400 * (11.57/11.57) 0.0000115 = 11.57/1000000 0.0000115 = 11.57 ppm ... even Wikipedia says: "One part per million (ppm) denotes one part per 1,000,000 parts [...] or about 32 seconds out of a year." ... if 1 ppm is ~32 seconds per year, then 12 ppm is ~384 per year: a little over 1 per day :-) -- C Anthony