The previous answers are correct you can be at your home during the appraisal but it is not advisable and the appraiser will not tell you what the value is. What I may suggest is you have your realtor there with several comps of homes in your area that support thae value you are selling it for. Withthe new appraisal rules it is not unheard of to have an appraisal from another area come to your home with little to no knowledge of the area who then submits an apprasial that comes in under value. I'm sure this is what you are trying to avoid.
Good luck with the sale.
Yes, you can be home. The appraiser will not have any results he is there to measure and compare your home to the other homes they have selected as possible comparables. He may also inspect some items like heating, flooring, holes in drywall etc. I would suggest that you not be present and let them just quickly do their job and leave.
You are allowed to ask for anything but the appraisal by law can not be shared with you by the appraiser or the buyers lender, but you can ask.