Hi, I hope this is helpful!
I have a Sunbeam Crocker Cooker Fryer... no idea what year it was manufactured, but it was my mother's, and judging from the colors, it's from pretty close to when yours was made. It also has that dial... Off, Simmer on the left side, then the red band in the top middle, then 300, 350, and 400 degree marks on the right side.
Anyway, the front panel on mine has temperature "instructions!" I don't know how that would fit into high and low (I'd guess low is just the simmer setting, and for high you just get to pick a more specific temperature setting). I'm sure you can guess from whatever you're cooking with in your recipe what setting to use according to this though. The instructions on the panel of mine read:
CROCKERY COOKING
USE ONLY CENTER RED BAND OF TEMP. DIAL
Beans.............12-14 hours
Chili................12-14 hours
Meat Sauce........8-9 hours
Stews...............8-10 hours
Soups...............6-12 hours
COOKING
Chicken 300 until boiling simmer 3-4 hours
Corned Beef 300 " " " 45 min./lb
Stews 300 " " " 1-2 hours
Vegetables 300 " " " until tender
Pot Roast 325-350 until brown " 2-3 hours
DEEP FRYING
Chicken 350-375 10-20 minutes
Chops & Cutlets 350-375 8-12 minutes
Doughnuts 375-400 2-4 minutes
French Fried Potatoes 375 10-15 minutes
Shrimp 375 1-4 minutes