I am going to focus on the 3 dBA exchange rate as it is what we use in BC, and in most provinces in Canada. There is an example of the 5 dBA rate in your text book that is used by some provinces and the US if interested. Most consider 3 dBA rule the more logical since with noise exposure we are more interested in total daily dose then it seems natural to divide the exposure time in half if the exposure doubles… results in same total dose.
Sometimes we are unable to measure dose with a dosimeter. However, it is still possible for us to estimate dose if we know: The duration of time spent doing various tasks throughout a shift The noise level during those tasks