POSIX realtime extensions have been developed to be high reliable.
(...) However, they offer no guarantees on interval measurements, and the correction algorithms can cause the measurement of a time interval of an hour or so duration to be off by +/- 1 sec, especially within the first few hours after a cold boot. (...)
At the start of this thread, my assumption was that all computers had a 100% reliable tick counter. Well, this shows I understand nothing about hardware. My problem is that the equipment I interact with is supposed to deliver data at a constant rate. Since I don't know how much its engineers care about patients, I wanted to be sure not to save wrong information. It wouldn't matter if the clock is saying we are on XVII century, as long as 10 seconds would never be 10.1. But, as I learned from you, my PC is not to be considered as a reference. Maybe the right approach is to ask people who understand hardware if mine is actually a valid concern. Thanks, Maurício