进行数学运算是否有原因* 1000/1000没有意义

Question

I am looking at this line of code and I cannot make sense of it. This particular code is javascript, but I eventually would like to make a java android app.

$("#TxtHalfDot").val(Math.round((60000/bpm)*3*1000)/1000); 

         //bpm being a user entered value

I understand the process of the math and have been through it with a calculator many times. However, I can not make sense of the *1000 followed by /1000.

My Question

Is this a strange behavior of the "math.round" function or is it just simply not needed. I have seen it a lot but when I look at it I feel it can be omitted, but I am not a computer...

(60000/bpm) * 3 gives the same result ((60000/bpm) *3*1000)/1000

Answer 1

If you look carefully you find that the whole term is divided by 1000 after rounding.

So it is not just x * 1000 / 1000 .

Answer 2

Math.round(a*1000)/1000 results in number a rounded with 3 decimals.

Ex: Math.round(1234.123456 * 1000)/1000 = 1234.123

How this works is like this: Suppose the number a has x decimals (in our example 6). You multiply the number by 10 to the power of n (in our example 3), effectively moving the decimal point n digits to the right. Then you round the number (cut all decimals). Then you divide by 10 to the power of n , moving the decimal point back.

Answer 3

It has to do with the parentheses.

Math.round((60000/bpm)*3*1000)/1000

In full it reads..

Divide 60000 by bpm then multiply by 3000 then perform Math.round then divide by 1000

You are rounding a possible float before dividing it by 1000