Pain specialist responsible for the acute pain service will assess patients' condition during daily ward round while patients are using patient controlled analgesia (PCA) device, receiving epidural infusion or peripheral nerve local anaesthetic infusion. For the pain assessment, patient will be asked to rate their current pain level using verbal numerical rating scale (NRS) as a standard or care. (0 being no pain, 10 being worst pain imaginable) Within one minute, the patient will be asked by the investigator, who is blinded to the verbal NRS, to rate the current pain level again on an electronic version of visual analogue scale on iPad® (vasQ Clinical©, Maki NAKATA 2011) The electronic VAS displayed on iPad® is a horizontal scale with "No Pain" on the left, "Worst Pain Imaginable" on the right. Patient can use the finger to mark the level of pain on the iPad® screen by moving a diamond shape marker alone the horizontal line. The length of the scale is divided electronically into 100 equal parts. There will be 101 possible score (0 - 10.0, which indicate the distance of the diamond marker from the left end of the scale. The score will be stored together with the patient's identifier.