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 a simple financial ratio that shows how much of your periodic revenue is left after you subtract costs of goods sold, or COGS. On a monthly revenue of $40,000 and COGS of $25,000, your gross margin is the $15,000 gross profit divided by the $40,000 revenue. This equals 0.375, or 37.5 percent. In essence, 37.5 percent of your revenue remains after COGS are removed, and before you remove operating costs and recognize irregular revenue and expenses.