I know the Burtonsville Amish Market as well as being from the Lancaster Amish markets in Pennsylvania.
Sorry I cannot give you absolute measurements. I am over 70 and I don't measure many things.
Make your mayonaise sauce...
Mayo, minced onion, minced celery.
(optional- minced parsley is optional)
(optional- 1 or 2 diced hardboiled eggs)
Add a couple of tsp of white vinegar. Salt and pepper to taste.
Some cooks add a bit of sugar...yuk. I hate sweet potato salad;
Boil the potatoes in lightly salted water. Drain when done. Put the warm potatoes in a large bowl. Pour the sauce over the warm potatoes and gently mix. Refrigerate. The flavor develops over time in the refrigerator. The warm potatoes absorbs the sauce, so make plenty of sauce.