What type of grid error occurs only when a focus grid is not placed right side up?

When a focus grid is not positioned correctly with the right side up, the type of grid error that occurs is referred to as "upside-down." This specific error happens because focus grids are designed with specific characteristics that direct the path of the x-rays. If the grid is flipped, the primary rays do not align properly with the grid lines, leading to significant distortion of the image.

An upside-down grid results in poor image quality, including a loss of contrast and increased visibility of grid lines on the radiograph. It is crucial for imaging professionals to ensure that the grid is oriented correctly, as this directly affects the quality of the diagnostic images produced.

Other grid errors, such as off-center, off-level, and off-angulation, pertain to misalignment in other ways, often related to the positioning of either the patient or the x-ray tube concerning the grid. However, they do not specifically arise from the grid being upside down, which highlights the unique nature of this particular error.