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.
Calculate the return for a direct-mail campaign by multiplying the four key elements: sale price, number of mailings, response rate and conversion rate. The response rate is the number of people who respond to an ad; the conversion rate is the number who make a purchase.