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.
The contribution margin is the amount of profit or loss that is above or below the break-even point on a per unit basis. This formula is usually used to show the amount of profit the company has after the break-even point has been passed. In the BEQ Equation, P-VC is the contribution margin.