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.
Tip. 1  You may also calculate the overhead rate based on direct labor hours. 2  Divide the overhead costs by the direct labor hours over the same measurement period. 3  In the example, the overhead rate is $20 for each direct labor hour ($2,000/100). Divide the overhead costs by the direct labor hours over the same measurement period. 2  In the example, the overhead rate is $20 for each direct labor hour ($2,000/100).