Figuring out what operator to use

A quick learner from Sacramento, CA says:
You have two types of cranks, one with a single arm ( Wood-Window-Crank-9-inch/pd/Casement-Window-Replacement-Operators/39-020 ) and one with two arms ( EntryGard-Operator-9-1_2-inch-Arm-Left-Handed/pd/Casement-Window-Replacement-Operators/39-031 ). In what situation do you use the one arm vs the two arm?

I have an old 1929 house that has push-out casement windows that I want to add hand crank operator and want to order the correct one. Thank you.
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Tom from SWISCO responded:
Could you send us some photos to better assist you and find the right operator? Thank you!
A quick learner from Sacramento, CA says:
Here are some pictures.
User submitted photos of a window operator.
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Dave Sr. from SWISCO responded:
Thank you! I believe the 39-031 operator would be a lot more work to install. You might be better off using something like the 39-020, along with the 39-520 track. We also have the older style 39-077 push bar and the older style 39-268 operator. I feel that one of these would be a better choice being that they are a made to be use with old style wood windows like you have.
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