Some arrangements provide for "accelerated vesting", by which all or a major portion of the unvested right vests all at once upon the occurrence of a specified event such as a termination of employment by the company or acquisition of the company by another. Less commonly, the vesting schedule may call for variable grants or subject to conditions such as reaching milestones or employee performance. "Graded vesting" (vesting after each year until the employee is fully vested) may be "uniform" (e.g., 20% of the compensation vested each year for five years) or "non-uniform" (e.g., 20%, 30%, and 50% of the compensation vested each year for the next three years).