How the elephant got its trunk...

Do you know the difference between truncating and rounding numbers?  Well take the famous number pi - 3.14158265....  Suppose we truncate this to four decimal places. This simply means that we drop all the decimal places beyond the fourth - so it becomes 3.1415.  Rounding to four decimal places on the other hand means that we express it to four decimal places, but the fourth decimal place depends on the fifth decimal place - if this is 0 to 4 then the fourth decimal place remains as it is, but if it is 5 to 9 then the fourth decimal place is rounded up one,  So rounded, it becomes 3.1416.