A faithful reader of these Tips called with a question that had caused controversy at his company. The question dealt with the most appropriate way to measure the 16±0.2 dimension. Some thought that the measurement should be oriented relative to Datum A as is shown in Figure 1. Others thought that since the dimension is shown from the top of the part, the measurement should be made oriented relative to the top as shown in Figure 2. The approach taken would make the difference between acceptance or rejection of the parts. The real answer is the Standards don’t clearly define what toleranced dimensions mean when used to locate surfaces like this. It could be interpreted differently depending on whether you are buying or selling. Figure 1 is not appropriate since there isn’t anything to relate the dimensions to datum A. Figure 2 is a possible interpretation, but it isn’t the only one. The variation of the measurement can change depending on which feature is used to establish the orientation of measurement.