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.
1. Calculate the contribution margin of one unit of each product by deducting the variable cost of one unit from its selling price. For example, if a unit of product A sells for $10 and it has variable costs of $4, its contribution margin per unit is $6. 2. Calculate the percentage of total sales mix that each product accounts for.