I didn’t add any constraints between the items in the stack view, I just set the contents of each label & text field to be center aligned and figured that was sufficient. The control dragging performed on page 233 was only necessary to get the leading edges of the text fields aligned because there was something else to the left of them throwing off the alignment. In World Trotter, each item is by itself in one of the vertical stack view cells with nothing to the left of it; if you set the vertical stack view Alignment attribute to Fill, the labels & text fields take up the entire width of the stack view which is enough to align them.
Judging by your picture, it looks like you aligned the leading edge of the text field to the center of the “degrees Fahrenheit” label. Or perhaps the text field contents are set to right align?