ruled line
罫 centers on a ruled line, the kind used to guide writing or divide a page into orderly rows and columns.
罫 combines 罒 (net) with 卦 (divination sign), but the exact historical development is uncertain. The modern meaning of ruled line may derive from the idea of a net-like grid.
The top 罒 looks like a net of horizontal and vertical lines, and the bottom 卦 resembles a set of marks. Together they suggest a ruled line drawn to create a grid.
For ケイ, imagine a ruler making a crisp, straight line with a sharp 'kay' sound: kay -> ケイ, like the edge of a ruled line.
—