the low point of the U or V-bottom well. The transition from agglutinated to non-agglutinated wells occurs distinctively, within 1 to 2 wells. The relative concentration, or titer, of the virus sample is based on the well with the last agglutinated appearance, immediately before a pellet is observed. Relative to the initial viral stock concentration, the virus concentration in this well will be some dilution of the stock, for example, 1/40-fold. The titer value of that sample is the inverse of the dilution, i.e., 40. In some cases, the virus is initially so dilute that agglutinated wells are never observed. In that case, the titer of these samples is commonly assigned as 5, indicating the highest possible concentration, but the accuracy of that value is clearly low. Alternatively, if the relative concentration of the virus is extremely high and the wells never transition to a button appearance. The titer value is then commonly assigned to be the highest dilution, such as 5120. HI is closely related to the HA assay, but includes anti-viral antibodies as “inhibitors” to interfere with the virus-RBC interaction. The goal is to characterize the concentration of antibodies in the antiserum or other samples containing antibodies. The HI assay is generally performed by creating a dilution series of antiserum across the rows of a 96-well microtiter plate. Each row would usually be a different sample. A standardized amount of virus or bacteria is added to each well, and the mixture is allowed to incubate at room temperature for 30 minutes. The last well in each row would be a negative control with no virus added. During the incubation, antibodies bind to the viral particles, and if the concentration and binding affinity of the antibodies are high enough, the viral particles are effectively blocked from causing hemagglutination. Next, a standardized amount of RBCs is added to each well and allowed to incubate at room temperature for an additional 30 minutes. The resulting HI plate images usually progress from non-agglutinated, “button” wells with high antibody concentration to agglutinated, red diffuse wells with low antibody concentration. The HI titer value is the inverse of the last dilution of serum that completely inhibited hemagglutination. The preceding descriptions of the HA and HI processes are generalized, and specific details can vary depending on the operator and laboratory. For example, serial dilutions across the rows is described, but some laboratories use an alternate