Hand positions

Gassho

Put your palms together, with fingertips at eye level.  Hands are one hand-width from your nose.  Elbows are held out slightly from the body.

Shashu

Fold your left thumb into your left palm and curl your fingers over it to make a fist.  Cover your left hand with your right and hold your hands in front of you against the body, with forearms parallel to the floor.

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Holding a chant book

It's always fine to use a book for chanting, even if others know the text by heart.  There's no need to hide or minimize your book, or to try somehow to balance it on your knee or zabuton to put your hands in some other position while chanting.

Sit up straight and hold your book upright in front of you, with the three middle fingers on the outside and thumb and little finger on the inside.  Keep your book on your zafu or otherwise avoid putting it on the floor when you're not using it.   

If you’re not using a book during chanting, put your hands in gassho or the cosmic mudra (hokkaijoin) as appropriate..

Isshu

Fold your left thumb into your left palm and curl your fingers over it to make a fist.  Cover your left hand with your right and hold your hands in front of you against the body, with forearms parallel to the floor.  Turn your hands so that the back of your hand is up and the palms are down.