The resistance in the leads to the RTD (resistance temperature device) may significantly affect accuracy. To deal with this problem, connection arrangements are available which allow the lead resistance to be measured and compensated for. From top to bottom they show:
2 Wire RTD Arrangement
3 Wire RTD Arrangement
4 Wire RTD Arrangement
4 Wire Compensated RTD Arrangement
With the 4 wire compensated arrangement you can obtain a very high resolution of temperatures around ambient.