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. Gross margin represents the percentage of net sales that the firm takes in as gross profit. It equals gross profit divided by net sales. If you have sold $500,000 worth of product, and the cost of goods sold is $300,000, the gross profit is $200,000. The gross margin is $200,000 divided by $500,000 which equals 40 percent. A business should not focus on gross margin exclusively, since you can increase gross margin but end up with less in gross profits. If your gross profits drop to $170,000 and sales decline to $400,000, gross margin would be higher, at 42.5 percent, yet gross profits would be $30,000 lower. Contribution Margin Contribution margin is a more relevant measure to assess the profitability of additional products sold, and only takes into account variable costs.