# Re: Ambiguous coordinates on T axis

```Hi Steve,
When you do a calculation over time when there are two different
time axes involved in the expression, Ferret gives this informational
message just to let you know that the two time averages are different.
It's using each variable's time axis and is doing the calculation you
expected. You could make it absolutely clear what you're doing by
specifying the time interval as a qualifier for each variable, in square
brackets.  (I use the backslash continuation character here)

yes? shade aglt[D=1,T="01-JAN-1994":"12-DEC-1994"@AVE]- \
aglt[D=2,T="01-JAN-1994":"12-DEC-1994"@AVE]

See "region" in the Users Guide index; this is the third way to specify
a region and is almost always the best way to be sure you're doing
what you think you're doing. And, this is also the way to do it if you
want to compare averages over two different time intervals:

yes? shade aglt[D=1,T="01-Jan-1994":"12-Jun-1994"@AVE]- \
aglt[D=2,T="13-Jun-1994":"12-Dec-1994"@AVE]

Ansley Manke

Steve Knox wrote:

> How can I avoid this ambiguity on the time axis when I'm dealing with 2
> datasets?
> I guess it's confused since it dosen't know which T axis to average over.
> In this case the time periods are the same so the ambiguity doesn't
> matter, but if I want
> to specify  different time periods in each dataset how can I do this?
>
> yes? use agltHistoric.cdf
> yes? use agltCENT.cdf
> yes? shade/T="01-JAN-1994":"12-DEC-1994" aglt[D=1,L=@AVE]-aglt[D=2,L=@AVE]
>
> *** NOTE: Ambiguous coordinates on T axis: AGLT[D=1,L=@AVE]-AGLT[D=2,L=@AVE]
>
> Thanks for any help on this.
>
> Steve Knox
> NREL
> Colorado State University

--
Ansley Manke  Pacific Marine Environmental Laboratory  Seattle WA

```