"...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.