Fields
The number on the right of each row is the protobuf field number.dateuint321
The trading date as days since 1970-01-01
expiryuint322
The expiry of the chain as days since 1970-01-01
skewdouble3
The put implied volatility minus the call implied volatility at the given delta. A positive value means puts are more expensive than calls
deltauint324
The delta bucket as a whole number out of 100. 25 means the 0.25 delta and 10 means the 0.10 delta.