Inch Time Foot Gem

A lord asked Takuan, a Zen Teacher, to suggest how he might pass the time. He felt his days very long attending his office and sitting stiffly to receive the homage of others.

Takuan wrote eight Chinese characters and gave them to the man:

Not twice this day
Inch time foot gem.

This day will not come again.
Each minute is worth a priceless gem.

COMMENT: I don't understand what Inch time foot gem means. Do any of you have an idea?