HI, I AM A LITTLE CONFUSE IN TERMS O THE MEASUREMENTS ON THE BOOK.
I DO NOT UNDERSTAND WHE ROSE REFERS TO 3 EGGS OR 21/2 OZ. FOR EXAMPLE.
I AM READY TO GIVE IT A TRY BUT I NEED TO UNDERSTAND HOW TO DO IT.

PLEASE GIVE ME SUGGESTIONS. I AM DYING TO TRY THE MUSSELINE BUTTERCREAM,

Try getting a scale.
I bought the book recently and found that the scale is really helpful. I purchased a digital scale from Walmart for about $20.

Plus I heard that weighing ingredients are more accurate. HTH

I was just thinking about this yesterday. The standard weight for a large egg (not including the shell) is 1.75 ounces. One large egg white weighs 1.05 ounces. I didn't realize how I took "Grade A Large" eggs for granted until I moved to a place where the eggs can range in size from teeny to "oh, my lord, that poor chicken" . If I didn't weigh them, there's no telling what I'd end up with!

So, I just looked at the recipe for Mousseline Buttercream - it calls for just egg whites. You need 5.25 ounces of egg whites (or 5 large egg whites).

I got my scale at Bed, Bath, and Beyond. It wasn't too much and I used one of their coupons that they always have.