My first spreadsheet is a calendar of sorts with date in one column and value
in next. Dates for different months are in different columns, so we have:
Date (Jan)| Value| Date (Feb)| Value| Date (Mar)| Value| etc.

My second spreadsheet references this "calendar" but the layout is not the
same at all (so lookups probably can't work?). In this spreadsheet, I have a
list of various dates from different months. What formula can I use to
return the corresponding value for the date, based on the source info in my
first spreadsheet?