HP 35s Scientific Calculator - Manual (Page 45)

Getting Started 1-29
Clearing All of Memory
Clearing all of memory erases all numbers, equations, and programs you've
stored. It does not affect mode and format settings. (To clear settings as well as
data, see "Clearing Memory" in appendix B.)
To clear all of memory:
1. Press  (). You will then see the confirmation prompt    ,
which safeguards against the unintentional clearing of memory.
2. Press Ц ()  .