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.
Therefore, total variable costs per unit are 50+10+15 = $75. Contribution margin per unit is 100 - 75 or 25. if we sell 20 units of product, total revenues are $2,000 [20 * 100] and total variable costs are 75 * 20 or $1,500.total contribution margin is 2,000 - 1,500 or $500.ontribution margin [CM] is defined as the difference between revenues and variable costs. CM can be calculated on a total or per unit basis. Assume we have a selling price of $100/unit and per-unit variable costs of $50 for labor, $10 for supplies, and $15 for sales commissions.