1. The problem statement, all variables and given/known data I have this problem for my homework: Time standards are now based on atomic clocks. A promising second standard is based on pulsars, which are rotating neutron stars (highly compact stars consisting only of neutrons). Some rotate at a rate that is highly stable, sending out a radio beacon that sweeps briefly across Earth once with each rotation, like a lighthouse beacon. Suppose a pulsar rotates once every 1.610 431 448 872 75 ± 4 ms, where the trailing ± 4 indicates the uncertainty in the last decimal place (it does not mean ± 4 ms). How many times does the pulsar rotate in 30.0 days? 2. Relevant equations This should just be a basic conversion, but I'm doing something wrong here. 3. The attempt at a solution I've attempted to convert the rotation period to seconds by dividing by 1000 first (1 ms = 1 x 10^-3 s, yes?). Then I calculate how many seconds are in 28 days: (30 x 24 (hours/day) x 60 (minutes/hour) x 60 (seconds/minute)) = 2592000 seconds I thought I could just take the number of rotations per second and multiply it by how many seconds are in 30 days. 0.001610413... x 2592000 = 4174.19 rotations in 28 days. I submitted this answer to my online homework and it was marked wrong. It said the answer is 1.61 x 10^9. Can anyone please show me what I did wrong here?