Your POS says how much sales fell, but the cause is usually in three numbers nobody writes down: walk-ins, walk-outs and table turnover.
Sales are the result, not the cause
When sales drop, what the owner sees is the final number. But sales come from several steps in a row: how many people walked in, how many got a seat, how long they stayed, and how quickly the table was free again. If you do not know which step changed, all you can do is guess.
Number one: walk-ins
If fewer people are walking in, the problem is outside the restaurant, such as location, how visible the shopfront is, or marketing. Speeding up service inside will not help.
Number two: walk-outs before seating
If walk-ins are the same but some groups come in and leave within a few minutes, the restaurant is losing customers who had already chosen to come. It usually happens when every table is full or there is nobody to greet them. Your POS has no way of knowing this number, because no bill is ever opened.
Number three: table turnover
If walk-ins are the same and nobody is leaving, but sales are still down, look at table turnover. Tables left dirty for a long time, or food that comes out slowly, mean fewer rounds of guests during the busy hours.
Put these three numbers next to your sales, and the question of why sales dropped has an answer that points to something you can fix.