In general the design of the mechanism is pretty simplistic. The servo is directly attached to an arm that rotates upwards to lift the weight and the body is built so as to remain as rigid as possible.
The maximum torque of the servo is 42 oz-in (2.725 lb-in) and the weight itself is one lb. Given that the distance from the servo to the weight is 2 in, a torque of only two lb-inch is required initially (2/2.725th of the maximum strength of the servo; about 73.39%.) As the weight is lifted, the distance from the servo to the weight decreases (up until the two are at the same height) and then increases back to the 2 lb-inch.
The servo, assuming it rotates a full 100 degrees, should lift the weight 2*2sin(50 degrees) or about 3.064 in.
The mechanism is pretty simplistic for the most part. It's about as straightforward a design as you can get.