如何在Ajax中从任何Api获取数据时计算获取时间

1. I just want to show the amount of data fetched from Api.

2. output should be like 10% fetched 90 % remaining like that.

3. I'm searching how should I calculate the amount the amount retreived and remaning data left to be fetched.

4. I have been working on basecamp api It would waste lots of time to fetch tasks , activities etc. So just want that I want to show time left while fetching in Ajax .

I have googled and found a link: Monitoring_progress but if any body could suggest to me where to start I would much appreciate.