YSI Pro20 - Manual (Page 7)

5) Place the battery cover on the back of the instrument and tighten the four
screws. Do NOT over-tighten.
The waterproof instrument case is sealed at the factory and is not to
be opened, except by authorized service technicians. Do not
attempt to separate the two halves of the instrument case as this
may damage the instrument, break the waterproof seal, and will
void the warranty.
KEYPAD
L
3
4
5
6
1
2
Figure 1, Pro20 with battery cover removed. Note battery symbols indicating
polarities.
Figure 2, keypad
3