This counts partial (incomplete) frames the card discarded because one or more of their constituent BTUs went missing in transit across the Cell Bus, and this object sets how many such incomplete frames per minute must occur before a trap fires. Missing BTUs mid-frame point to backplane contention or a card losing sync with the bus, so this threshold lets you catch reassembly failures on this card specifically before users notice dropped frames. Setting it to 20 would mean the card stays quiet until it discards more than 20 incomplete frames within any one-minute window, enough to filter normal noise but catch a real backplane problem.