This question would be easy for anyone who has some tech experience with stopwatchs.
I'm going to make some measurements. and I need a 1ms accuracy stopwatch.
I found one that could do the work with the following specificacions : Accuracy (time): ±30 seconds per month (stopwatch): 99.9988% Based on the document stopwatch and timer calibrations 2009 (National inst. of standars and tech) http://tf.nist.gov/general/pdf/2281.pdf , I used thier formula to try to find out the accuracy in milliseconds.
x1/day * x2 Where x1 is the original resolution in seconds and x2 is the new interval to compute in seconds. In the particular of the stopwatch i want to buy: x1/month * 1/(2592000/x1) month 30/86400 = 0,000347222222 sec.
This is my problem: The document suggest to have caution using the formula for less periods of time than the tech specifications shows. so In this case I used 30 seconds intervals instead of 1 month. (my measurements will be done in 30 seconds intervals).
Now 0,000347 obviously is not the resolution.
But How can i know that the stopwatch has a resolution of 1ms or better?
Seems like I'm stock and I can't find out a way to solve this problem.
UPDATE: I'd like to keep the focus of the question in how to know the actual accuracy of the device, the use of the formula provided by the document mentioned abovea and it's limitations. thanks