We appreciate the need to be realistic about this. The same person could watch a student taking three different blood samples from three different patients, potentially on the same day. This is acceptable; after all, each patient is different. The point is that you need to be signed off doing each thing three different times. If the same person signs you off three times and/or these are all on the same day, we would recommend that your commentary notes/reflections make some reference about the context and setting. Ideally, and from a strictly educational perspective, it is good to have different observers but we understand that that is not always practical or possible.