how did they calculate the speed of light before they had sophisticated gadgetry?

Question

...like back in the 1600's?

Answer 1

By knowing what they were doing, and doing it very precisely.
Check out http://www.speed-light.info/measurement.htm


Doug

Answer 2

The first appropriate calculation of the speed of light was by an astronomer named Fizeau, who was observing the moons of Jupiter. The moons were not transiting Jupiter at the expected time, and Fizeau correctly deduced that the differing distance between earth and Jupiter, in conjunction with the speed of light, was the reason. The size of the astronomical unit was known fairly well by that time, so he got a reasonably decent answer.