Question: As per the ALS PCS, why is there a deliberate gap between normotension and hypotension?

Question: I was faced the other day with a question by one of my fellow peers in regards to the administration of nitroglycerine. As a contraindication, it states that we cannot administer nitro of the SBP drops by one third or more of its initial value after nitro is administered. This can be interpreted in 2 different ways, as brought to my attention by my fellow peer so now ever since, I second guess myself. So my question is, this “initial value,” is it the very first BP we take even before the first dose of nitro, or is it referring to the initial BP you take AFTER the first dose of nitro. It is such a simple answer I am sure but if I can get clarification so I can also relay the message to my fellow peer that would be great.