Environment affects Timing
Actel uses derating factors for timing values. A derating factor is a multiplication factor applied to the timing value.
Notice that fastest timing (smallest derating factor) is for high Voltage, low temperature. The slowest timing (largest derating factor) is for low voltage, high temperature.
Four corners: (low temp, low vdd), (high temp, low vdd), (low temp, high vdd), (high temp, high vdd).