It's a spare part in case yours gets damaged. They really do not want you to run the machine without adequate lube, so they include one just in case. When you do the first oil change, carefully remove the one that is installed and clean it with a rag and when you replace the lube with something a bit more clear and much better quality than the fish oil they use in china it will be just fine. Keep that spare someplace where you can find it because I know for a fact that they are a damage magnet on a late Sunday afternoon when there is no chance of even trying to get something to temporarily fill the hole to keep the juice inside. Don't ask me how I know, but suffice it to say I learned this lesson the hard way. If you ever have to replace the sight glass order another and keep it for a spare when it arrives. That way your Sunday project will never be ruined by a .20 cent part. Hope this helps to get you going and keep you going for a long long time.
Bob.
And just for the record, I want one of them so bad I can hardly stand it...so I am jealous!!!!