(a) for transactions with employees and others providing similar services, the entity is required to measure the fair value of the equity instruments granted, because it is typically not possible to estimate reliably the fair value of employee services received. The fair value of the equity instruments granted is measured at grant date.
(b) for transactions with parties other than employees (and those providing similar services), there is a rebuttable presumption that the fair value of the goods or services received can be estimated reliably. That fair value is measured at the date the entity obtains the goods or the counterparty renders service. In rare cases, if the presumption is rebutted, the transaction is measured by reference to the fair value of the equity
instruments granted, measured at the date the entity obtains the goods or the counterparty renders service.