# [arch-general] Leap seconds ntp and chrony?

C Anthony Risinger anthony at xtfx.me
Fri Jul 6 11:38:15 EDT 2012

```On Thu, Jul 5, 2012 at 1:16 PM, Kevin Chadwick <ma1l1ists at 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
```