Dotcom-Monitor offers per-hour billing for using Load Injector Servers (LIs): 

Load Injector Hours  = ∑ LIs Time

Load Injector Time is a server operational time calculated from the Load Injector Server boot up till the end of the test.

For on-demand tests, the actual Load Injector Time will be rounded up to hours due to the mechanism of LIs operation. For example, for the test of 20 minutes duration run on 10 Load Injector Servers (including Reference Server), the Load Injector Hours = 10 × 1 hour = 10 hours. So you will be charged for 10 Load Injector Hours.

 In the case of SmallMedium or Large plans, the actual Load Injector Time is considered to calculate Load Injector Hours. For example, for the test of 20 minutes duration run on 10 Load Injector Servers (including Reference Server), the Load Injector Hours = 10 × 20 minutes = 200 minutes or about 3.3 hours. In this case, 3.3 Load Injector Hours will be written off from your resource wallet.