A drug delivery device comprising: a housing; a dose sleeve located within the housing, the dose sleeve being configured to move helically within the housing as a medicament dose is dialled into or delivered from the drug delivery device; a dose setting arrangement coupled to the dose sleeve and configured to cause helical movement of the dose sleeve as a medicament dose is dialled into the drug delivery device through rotation of a dose dial member forming part of the dose setting arrangement; a dose delivery arrangement comprising a dose button coupled to the dose sleeve and configured to cause delivery of medicament with helical movement of the dose sleeve and without rotation of the dose dial member when the dose button is actuated; a first sensor arrangement for detecting a rotation of the dose dial member relative to the housing; a second sensor arrangement (138, 148) for detecting movement of the dose sleeve relative to the housing; and a processor arrangement coupled to receive inputs from the first and second sensor arrangements and configured to calculate therefrom the size of a medicament dose dispensed by the drug delivery device, wherein the dose dial member comprises features, the first sensor arrangement comprises a first sensor, the first sensor comprising first and second sensor components (136a, 136b, 136a-S1, 136b-S2, 136-S1, 136-S2) located such as to detect the features of the dose dial member as the dose dial member rotates, and characterized in that the processor arrangement is configured to calculate from a phase of signals provided by the first and second sensor components (136a, 136b, 136a-S1, 136b-S2, 136-S1, 136-S2) the direction of rotation of the dose dial member. a housing; a dose sleeve located within the housing, the dose sleeve being configured to move helically within the housing as a medicament dose is dialled into or delivered from the drug delivery device; a dose setting arrangement coupled to the dose sleeve and configured to cause helical movement of the dose sleeve as a medicament dose is dialled into the drug delivery device through rotation of a dose dial member forming part of the dose setting arrangement; a dose delivery arrangement comprising a dose button coupled to the dose sleeve and configured to cause delivery of medicament with helical movement of the dose sleeve and without rotation of the dose dial member when the dose button is actuated; a first sensor arrangement for detecting a rotation of the dose dial member relative to the housing; a second sensor arrangement (138, 148) for detecting movement of the dose sleeve relative to the housing; and a processor arrangement coupled to receive inputs from the first and second sensor arrangements and configured to calculate therefrom the size of a medicament dose dispensed by the drug delivery device, wherein the dose dial member comprises features, the first sensor arrangement comprises a first sensor, the first sensor comprising first and second sensor components (136a, 136b, 136a-S1, 136b-S2, 136-S1, 136-S2) located such as to detect the features of the dose dial member as the dose dial member rotates, and characterized in that the processor arrangement is configured to calculate from a phase of signals provided by the first and second sensor components (136a, 136b, 136a-S1, 136b-S2, 136-S1, 136-S2) the direction of rotation of the dose dial member.