In Episode 1 of Amanchu!, Hikari bestows the nickname "Teko" on Futaba, with the following explanation.
Hikari: [Gazes longingly into Futaba's eyes]
Hikari: Wow! Your eyebrows are so thin. They're, like, one-tenth as thick as the average. One-tenth...Tenth...Teko! An adorable nickname!
How did Hikari hit upon this nickname in the original Japanese? And bonus question: the translation I read of the manga translated Futaba's nickname as "Dotty". Was this completely out of nowhere, or does it have some justification in the original?