1 Onset of sleep from time the lights were turned off; this is called  sleep onset latency  and normally is less than 20 minutes. ( 2 Note that determining sleep and awake is based solely on the EEG. Patients sometimes feel they were awake when the EEG shows they were sleeping.
The direct cost margin is calculated by taking the difference between the revenue generated by the sale of goods or services and the sum of all direct costs associated with the production of those goods, divided by the total revenue.
Net margin is net profit divided by net revenues, often expressed as a percentage. This number is an indication of how effective a company is at cost control. The higher the net margin is, the more effective the company is at converting revenue into actual profit.