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.
Contribution margin (CM) is the amount by which sales revenue exceeds variable costs. It can be calculated as contribution margin per unit as well as total contribution margin, using the following formulas:Unit CM = Unit Price â Variable Cost per Unit.Total CM = Total Sales â Total Variable Costs.t can be calculated as contribution margin per unit as well as total contribution margin, using the following formulas: Unit CM = Unit Price â Variable Cost per Unit. Total CM = Total Sales â Total Variable Costs.