Machine epsilon of the HP Prime

[Albert Chan]

For HP Prime, formal definition (maximum relative error) and variant definition (ulp of 1.) are the same.
CAS round number to 53 bits double (round-to-nearest), then chop to 48 bits,

u = maximum relative error = (1 ULP) / (2^47 ULP) = 2^-47

1 = 2^47 ULP, unaffected by rounding-mode.
This probably made variant defintion, ε = ulp of 1., more popular.