What measurement is crucial for proper gutter installation?

The measurement that is crucial for proper gutter installation is the distance between the high point of the roof and the downspout. This measurement ensures that water flows efficiently from the roof into the gutters and then down the downspout. Proper drainage is vital to prevent water accumulation, which can lead to various issues, such as roof damage, foundation problems, and landscape erosion.

When this distance is accurately measured and maintained, it ensures that the gutter system functions effectively, directing water away from the structure. This helps in reducing the risk of water damage to the building's foundation, siding, and landscaping, and promotes better longevity for both the gutters and the roof.

The other options, while relevant in different contexts, do not provide the same critical information needed for ensuring proper functionality of the gutter system. For example, the distance from ground level is not a direct factor in the gutter's ability to channel water, and distance between supports pertains more to structural integrity rather than drainage efficiency. Distance from the eaves is also important but primarily relates to where the gutters sit rather than their performance in directing water away from the roof.