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.
Gross margin is frequently expressed as a percentage, called the gross margin percentage. The calculation is: (Net sales-Cost of goods sold) / Net sales. For example, a company has sales of $1,000,000 and cost of goods sold of $750,000, which results in a gross margin of $250,000 and a gross margin percentage of 25%.