Ever since night vision scopes have been invented, it was obvious that there is one major inconvenience with these devices – the need to re-zero them every time the scope is switched with the day scope.
So, the owner would either need to have two dedicated rifles, one for daytime and one for the night, or they would have to re-zero their scopes each time they switched. Naturally, neither scenario is ideal. That’s how night vision clip-on scope attachments were invented.