Hi there,

We're using latest mongodb(2.2.36) packages with mongodb-core (2.1.20) and we found that "staleness" calculation is not valid in replset https://github.com/mongodb-js/mongodb-core/blob/3.1/lib/topologies/replset.js#L442

Problem is that process.hrtime()[1] is nanoseconds and in this formula should be

server.lastUpdateTime = hrTime[0] * 1000 + Math.round(hrTime[1] / 1000000);

Now, formula is result of sum of milliseconds and microseconds which is not correct. It affects secondary and secondaryPreferred read preference logics, and for now it is broken.
This bug seems to exist at all versions of driver.