Running response time tests on php code - how much is 7.2E-5 microseconds?

Hi guys I'm using microtime() function of php to tell how long certain snippets of code take to run I do this by taking the time before and after the snippet and subtracting them using microtime function.

I got the following results though for the different snippets:

1 -  0.022976

2 -  0.003656

3 - -0.196361

4-   0.006563

5-   7.2E-5

6-   0.847695

7-   0.005092

8-   7.6E-5

9-   0.08024

The first numbers represent the snippt and the following the time taken... I've fo开发者_如何学运维rgotten whatever I learnt back in College on numerical methods :( - how big is 7.2E-5 microseconds?

7.2E-5 = 7.2 x 10^-5 = 7.2 x 0.00001 = 0.000072

So 7.2E-5 microseconds = 0.000072 microseconds