Is hydromerter absolutely necessary?

First batch ever. Nut Brown Ale from Northern Brewer. So far, so good. Brewed yesterday, already evidence of fermentation less than 24 hours after start.

Can we just wait until visible fermentation has stopped (as described in watching the airlock for bubbles), OR is it absolutely necessary to use the hydrometer to take your readings 2 days in a row to see the consistency in the specific gravity.

Just so you know, the reason I am asking this is that the beer is actually over at my buddies house, and I'm not sure he knows how to use the hydrometer. I'd like to keep it simple if possible.

Classic questions deserve links to classic threads:

https://www.homebrewtalk.com/showthread.php?t=212

thanks a ton. I appreciate everyone's knowledge here. Sorry about the Packers on Thursday. I am a Cal grad and was actually pleasantly surprised at Aaron Rodgers performance. I know you guys love Favre, but hopefully, Aaron will be a worthy replacement when that day finally does come. I am hoping my Raiders will fare better this afternoon.

And just to cover all the bases, here is a recent thread.

without a hydrometer, its just guess work. sometimes the airlock never bubbles. sometimes the airlock bubbles even though fermentation has really, truly completed.