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.
Margin, or gross margin, is the difference between total sales and the cost of those sales. For example: If total sales equals $1,000 and cost of sales equals $300, then the margin equals $700. Gross-profit margin can be expressed in dollars or as a percentage.