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.
Compound Interest. Simple Interest. The formula for contribution margin is the sales price of a product minus its variable costs. In other words, calculating the contribution margin determines the sales amount left over after adjusting for the variable costs of selling additional products.o better understand contribution margin, consider that the net income of a company is its revenues minus expenses. The term revenues is synonymous with sales, and expenses include fixed costs and variable costs.