The faster it sells the closer to 1 the number is…
For books figure the following:
Under 1000: sells like a maniac, at the right price will sell within hours
Under 10,000: will sell within a week if priced right
Under 100,000: will sell within 1-3 weeks if priced right
Under 250,000: will sell within a month or two if priced right
500,000: Give it several months
1,000,000: Give it 6 months
2,000,000: Give it a year
3,000,000: Hope you’ve got time
4-8 million: could take years
9 million or higher: May never sell
All of this is a rough, rough estimate. Have sold books with a rank of 5 million within a week or two of sending in, have waiting weeks or months with rank of 25,000. It’s you and your mazel.
Textbooks will shift to a much more favorable rank during the months of January and August if they are still in prevalent use (they could go from 1 million during the off-season to 50,000 or less etc.)
Take care.