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 can be determined at the unit level, as well. Doing so tells you how much each individual unit contributes toward fixed costs and profit, which is a more useful figure for production planning. To get the per-unit margin, divide the product's total contribution margin by the number of units produced. Say you have a total margin of $15,000 and you cranked out 12,000 units. Your per-unit contribution margin is $1.25.