Some writing isn’t measuring up in the gauge vs. gage department.
Gauge (with a “u”) relates to measuring. It can mean to measure (verb), instruments that measure (noun) or an actual measurement (noun).
Gage means an item that one offers to prove their pledge is serious (noun).
As the language evolves, gauge soon may become obsolete, at least in American English, where gage increasingly is used in its place. This probably has arisen because for some nautical terms, gage rather than gauge is used when referring to instruments that measure, such as weather gage and lee gage.
Bottom line: Until the shift in the language’s direction is complete, keep using gauge when referring to measurements.