Where should the preheat temperature be measured?

The correct answer indicates that the preheat temperature should be measured two to three inches from the groove. This practice ensures that the measurement reflects the actual conditions that the weld will face during the welding process. Preheating is essential to ensure that the base metal reaches an appropriate temperature, which can help reduce the risk of cracking and other issues during welding.

Measuring the temperature a few inches away from the groove allows for a more accurate representation of what the weld will experience as the heat from the arc will influence the metal in that immediate vicinity. This distance is close enough to account for the heat's effect but far enough to avoid any localized temperature spikes that may occur directly at the weld seam due to the intense heat of the welding arc.

The other options involve either measuring too close or too far from the groove, which may not provide an accurate assessment of the metal's preheat condition directly related to the welding process. Thus, measuring two to three inches from the groove is the best practice for effective welding preparation.