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.
On a per unit basis, contribution is calculated as: Contribution Margin per unit of sales = Sales Revenue per Unit-Variable Expenses per Unit. Contribution Margin-Fixed Costs = Net Operating Profit or Loss. The break-even formula calculates the point at which a company's sales are zero-there is no profit or loss:ontribution Margin per unit of sales = Sales Revenue per Unit-Variable Expenses per Unit. Contribution Margin-Fixed Costs = Net Operating Profit or Loss. The break-even formula calculates the point at which a company's sales are zero-there is no profit or loss: