Patrick,
You can redefine the axis, then for that Ferret session the new definition is applied to the dataset without changing the file. If you can come up with an _expression_ that describes 50 years of time in the units of the original axis coordinates, then it would look something like this, using a variable from the file that has the time axis.
yes? let tt = t[gt=`var,return=taxis`]
yes? define
axis/t/t0="`var,return=t0`"/units="`var,return=tunits`
`var,return=taxis` = tt_plus_50
Ferret will tell you it's replacing the definition of the axis.
Replacing definition of axis TIME
*** NOTE: grid used by data set mydataset
*** NOTE: Redefinition may alter apparent contents
of data set
The family of functions TAX* give us ways to extract information about calendar time axes which may prove useful in setting up the tt_plus_50 variable for the new coordinates.
I am not in the office and am unable to look up the details of the function DATES.
-Ansley