I have a tuning fork that belonged to my Grandad. He used one to get the pitch for the singing he led as priest of the Orthodox church he ran. I don't know if the one I have is one that he used but it could be.

Although it is stamped "C", when I check it with a tuner it is about 1/4 tone flat of B. More than a full tone lower than it says. The question is, is this a fault on the fork or could old pitch be that far out? Next question, if it is a fault should I try to fix it with a file?