Time values: units, zones, and calendars
Machine timestamps, local wall-clock times, and calendar dates answer different questions. Mixing them is the usual source of wrong answers.
Count digits on Unix values before converting: ten often means seconds, thirteen often means milliseconds. Compare UTC and local labels when a log line looks impossible.
Timezone converters should use named zones (for example America/New_York) rather than fixed offsets when daylight saving matters.
Use the Unix Timestamp tool as the main entry point for epoch conversion. Date and duration tools handle calendar math and elapsed time separately.

