Yashica MAT-124G - Battery Loading

1 - Open the Battery Compartment Cover holding with finger and
by turning it counter-clockwise.
This camera uses a 1.3 V mercury battery to power its exposure
meter. Use either Mallory PX-13B. Eveready EPX-13 or
equivalent.
2 - Install a 1.3 V mercury battery to power the exposure meter, as
illustrated.