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"...diners spent much less when menus used the word dollars or the dollar sign than when only numerals were used to indicate price."

The above quote makes me confused of the word "than" in "...the dollar sign than..."
I found this from an online article about "15 secret tatics of marketers."
What does "than" mean in this wording, and what roles is it playing in the whole context.
Is it correct in grammar as well as in writing?
Please help me understand more of this situation.
Thank you for your time.
Best regards!

Than is used to compare. In this case, we're comparing the amount people spent at restaurants with and without "dollar" indicated by the menu's prices. The text is saying that diners spent less money when the dollar sign was written with the price. They would spend less if the price of a meal were written as $17.99 than if it were written 17.99.