This is very principal of Hudson fan blade balancing technique to help you for understanding the quality of Hudson products. Hudson does not dynamically balance even the large fan assemblies in their factory, since Hudson have never found such balancing is necessary.

Hudson do statically balance the hub assembly, and each blade is moment balanced to a master standard. If fan assemblies must be dynamically balanced as a firm customer requirement, then this step must be accomplished at the job location. Note that it is highly likely that the structure surrounding the fans could also influence the final balance point, thus dynamic balancing of installed fans may infect, yield better result.

You have to know that the cost for dynamic balancing is the cheapest than one for static balancing, since its procedure is very simple. However, you have to dynamically balance the fan assemblies whenever to change the blades. Note that a way of statically balancing each blade is a best methods to reduce such inconvenience.

Hudson fans are component (each blade and hub) balanced as compared to whole fan assembly balance. This allows individual blades to be changed at job sites without rebalancing the whole fan assembly. Picture a hypothetical 2 blades fan from a side as the figure below.

Where, W₁ and W₂ are blade weight.
d₁ and d₂ are distance to center of gravity of blade.
F_c1 and F_c2 are centrifugal forces created by the rotating blades.

Centrifugal forces acting on a rotating system impels particles radically outward from the axis of rotation. If the masses of rotating components are evenly distributed about its shaft axis, the part is "balanced". To have a balanced system, there should be an equilibrium in centrifugal forces as follows:

F_c1 = W₁ x d₁ x (RPM₁) / g
F_c2 = W₂ x d₂ x (RPM₂) / g

For equilibrium in centrifugal force, F_c1 = F_c2.

Thus, it becomes W₁ x d₁ = W₂ x d₂, since RPM₁ = RPM₂.

From the above analogy, the equilibrium of centrifugal forces becomes the equilibrium of moments (weight x distance to center of gravity).

The Hudson computer controlled electronic balancing machine are used to balance the blades, and this machine will not print its serial number if a blade is out of Hudson manufacturing tolerance.