Hour Glass Problem : How can you calculate 9 minutes?

Answer of the puzzle How can you calculate 9 minutes is :

To get 9 minutes first let both the glasses run together. After 4 minutes first glass (4 minute) will be empty so turn/revers that and let it run again. At this point of time second  glass (7 minutes) will still be running.

After 3 minutes (total minutes measured so far is 7) second glass will be empty. Now turn/reverse that again and let it run.

After another 1 minute (total minutes measured so far is 8) once again first glass will be empty but the crux here is second glass has only run for 1 minute. What you need to do is immediately turn/reverse the second glass. The second glass will run for another 1 minute and that will be your total 9 minutes.

If you have another easy method do share in the comment section.