Accuracy of baby scales

My 1 year old daughter is petite. She is not underweight on my pediatrician's graph, but she is close. When I weigh her at home on my digital scale, she is consistently 2.5-3 pounds heavier than when they weigh her at the pediatrician. The nurse there uses a manual scale and I feel like there is room for interpretation error. It's frustrating to me that she is a much more normal weight at home (at various times of day, wearing just a diaper like she does at the doctor) but when it "counts" at the doctor she is 3 pounds less. That seems like a large difference in weight for someone so small.

Anyone else experience anything like this? I'm not sure I trust the manual scale at the doctor since it just relies on the way the nurse reads it.