Which type of alignment check is generally considered unreliable and infrequently used?

A hot check, which refers to aligning machinery while it is in operation or at its normal operating temperature, is often considered unreliable when it comes to precise alignment. This is primarily due to the expansion and contraction of materials caused by heat. When machinery operates, components can shift and distort slightly due to thermal effects, making it challenging to achieve an accurate alignment measurement. Since the conditions under which the measurements are taken (the operational state) are constantly changing, any readings obtained are subject to considerable variability.

In contrast, other methods, like cold checks (performed when the machinery is not operating and fully cooled down) and ambient checks (which observe machinery under normal environmental conditions), provide more stable parameters and generally yield more dependable results. Therefore, a hot check is typically infrequently used in professional settings where precision in alignment is critical.