I don't think you can.
A Detail will always be created at twice the scale of the plan that you place it in.
A Worksheet will always open at the same scale as the plan it was placed in.
Obviously if you then change the scale of either they will stay at that scale.
Even using Favourites or ALT-clicking an existing detail/worksheet will not set a default scale.
Barry.
One of the forum moderators.
Versions 6.5 to 27
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