Sundials were and are not that accurate, alas. There were too many variables in sun positioning during the year to make sundials useful for more than a give-or-take-an-hour guess of the time.
The quantum leap forward in time measurement took place in December 1656, when Dutch scientist, musician, and poet Christiaan Huygen invented the world’s first pendulum clock. The clock could run for about three hours with an error rate of as little as one second. This was a great improvement over earlier mechanical clocks, which could gain or lose that much every few minutes.
Huygen’s clock was also the first to have a second handbefore that, there hadn’t been much point in having one.
Huygen’s invention was pretty revolutionary. With improvements by others over the centuries, pendulum clocks remained the standard for accuracy for nearly 300 years.