when 60% of all eligible members must approve something, when a person who chooses not to vote, is his vote an abstention, a "yes", or a "no" vote?

[Guest Jane Moore]

if the contract language stipulates that 60% of all Eligible voters at a particular location must vote "yes' in order to make a change in a contract, how are the votes of the eligible voters who choose not to vote considered?

[Edgar Guest]

See FAQ #6.

[Gary Novosielski]

if the contract language stipulates that 60% of all Eligible voters at a particular location must vote "yes' in order to make a change in a contract, how are the votes of the eligible voters who choose not to vote considered?

They aren't considered.  The only relevant numbers are the number of Yes votes and the number of eligible voters at the location.  Abstentions are not the same thing as No votes, but in this situation they have essentially the same effect.