"Daylight A" was used with indoor Kodachrome film to convert it for outdoor daylight use. Type A Kodachrome was balanced for tungsten light, which is yellowy. The filter, which is nice yellowy-orange shade, made the rather blue daylight look yellow to the film, so the colors would turn out right. Note this is all in the past tense, since Kodachrome is no longer made.
What to do with a type A filter in the post-modern world? The yellow-orange color ought to make it work as a serviceable contrast filter for black and white shooting. How much to allow as a filter factor? I'll take a wild guess: 1.5 stops?? And bracket from there!
"If you always do what you've always done, you'll always get what you always got."
--Variously attributed to Moms Maybley, Mark Twain, etc.