Hello,

`qml.measure`

measures the qubit in the computational basis, which is the Pauli Z basis, I would say. But why do I get different results with `qml.expval(op=measurement)`

and `qml.expval(qml.PauliZ(wires=0)`

?

Below you can find a minimal working example:

```
import pennylane as qml
from pennylane import numpy as np
device = qml.device('default.qubit', wires=1)
@qml.qnode(device)
def circuit_pauli_z(params):
qml.RX(params, wires=0)
return qml.expval(qml.PauliZ(wires=0))
@qml.qnode(device)
def circuit_measure(params):
qml.RX(params, wires=0)
measurement = qml.measure(wires=0)
return qml.expval(op=measurement)
params = 0.75 * np.pi
result_pauli_z = circuit_pauli_z(params)
result_measurement = circuit_measure(params)
print(result_pauli_z)
print(result_measurement)
```

which gives:

```
-0.7071067811865475
0.8535533905932737
```

From my understanding, the first result is the expected one. But what is the second output (the one from `qml.measure`

?