HP Prime Graphing Calculator - Manual (Page 435)

Variables 431
Home variables
The Home variables are accessed by pressing a and
tapping .
Category Names
Real A to Z and 
For example, 7.45
A
Complex Z0 to Z9
For example, 2+3×i
Z1 or
(2,3)
Z1 (depending on your
Complex number settings)
List L0 to L9
For example, {1,2,3}
L1.
Matrix M0 to M9
Store matrices and vectors in these
variables.
For example, [[1,2],[3,4]]
M1.
Graphics G0 to G9
Settings HAngle
HFormat
HDigits
HComplex
Date
Time
Language
Entry
Integer
Base
Bits
Signed