I know this isn't exactly on subject, but I do a lot of horse sitting and the scoop issue can drive me crazy when people aren't specific, I'll be told to give "a scoop" of this or that only to find a wide variety of scoops sitting on the counter in the feed room in various sizes.
The worst is my neighbour who has a 1/2cp. Measuring cup she feeds with. Mare #1 gets 5 scoops with it, Gelding #2 gets 9 scoops, Gelding #3 gets 14 scoops for a grand total of 28 scoops! Seriously how much time does she think I have! I have tried to talk her into getting a bigger "scoop" but she refuses, she thinks this is more accurate(!?!) A rounded scoop vs. a level scoop in her case could double her feed bill.
She takes the cake for making me crazy when I pet sit!
In this case I'd buy my own 3 quart scoop to take with me for pet sitting. Then I'd measure how much each horse gets with the 1/2 c scoop, into the 3 quart scoop, and mark with a sharpie. I'd keep my scoop at home and bring it when I was pet sitting. Saves me time and hassle, doesn't require the OWNER of the horse to change her ways for the SITTER who is temporary.