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.
Below is an example of how straight-line depreciation can be calculated for a playground structure. 1  To calculate depreciation, we must first identify the acquisition cost, salvage value, and useful life. 2  If we apply the equation for straight line depreciation, we would subtract the salvage value from the cost and then divide by the useful life. The result would look something like this: ($21,500 â $0) / 20 years = $1075 annual depreciation