So if you read the POO, you see:

   - Communication between systems is facilitated by establishing a
   standard time origin that is the calendar date and time to which a clock
   value of zero corresponds. January 1, 1900, 0 a.m. Coordinated Universal
   Time (UTC) is recommended as this origin, and it is said to begin the
   standard epoch for the clock.



   - The time-of-day (TOD) clock provides a high- resolution measure of
   real time suitable for the indication of date and time of day. The cycle of
   the clock is approximately 143 years.



   - The TOD clock is a 104-bit register.


So, January 1, 1900 + 143 years = January 1, 2042, which is when the 104
bit clock will roll over, and bit 0 will return to zero.

Joe

On Fri, Dec 28, 2018 at 5:06 PM Paul Gilmartin <
[email protected]> wrote:

> In: MVS Interactive Problem Control System (IPCS) Customization
> Version 2 Release 3  SA23-1383-30
>
> I read:
> TOD Clock Service
>     The time-of-day (TOD) clock service provides a caller, including your
> exit routine,
>     with a TOD clock image. In the clock image, bit 0 is set on to allow
> the service to
>     handle values from May 11,1971, at 11:56:53.685248 to January 25,
> 2114, at
>     11:50:41.055743.
>
> ???
> But in PoOps I see
>     ...
>     If the programming support uses the standard epoch, bit 0 of the clock
> remains one
>     through the years 1972-2041. (Bit 0 turned on at 11:56:53.685248 (UTC)
> May 11, 1971.)
>
> I'm inclined to believe the latter, and that Bit 0 returns to 0, not 1, in
> September, 2042.
> Is there an error in the IPCS doc?
>
> -- gil
>
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