In academic contexts, these often refer to intermediate economics or Risk Management (ARM) designations.

"Incredibly challenging but essential. Passing 401 is a relief for anyone on the ARM journey, as it's often cited as the hardest exam. Highly recommend using a study group or a supplemental guide to get through the concepts." Aviation: Cessna 401 and 402

"Perfect for families or groups who want both togetherness and privacy. The lockoff between 401 and 402 is a game-changer. You get a full kitchen in the larger unit and a cozy setup in the second, plus you're just a three-minute walk from the slopes. Great proximity to local restaurants, though parking is a short drive away."

This specific vacation rental is highly rated for its mountain views and convenient "lockoff" setup, which connects two separate units.