HP 33s - Manual (Page 338)

D–14 More about Solving
Underflow
Underflow occurs when the magnitude of a number is smaller than the calculator
can represent, so it substitutes zero. This can affect SOLVE results. For example,
consider the equation
2
1
x
whose root is infinite in value. Because of underflow, SOLVE returns a very large
value as a root. (The calculator cannot represent infinity, anyway.)