# init(xStart:xEnd:y:) Creates a horizontal rule mark that plots a value on y. ``` nonisolated init(xStart: CGFloat? = nil, xEnd: CGFloat? = nil, y: PlottableValue) where Y : Plottable ``` ## Parameters `xStart` The x start position. If `xStart` is `nil` the rule will start at the leading edge of the plotting area. `xEnd` The x end position. If `xEnd` is `nil` the rule will end at the trailing edge of the plotting area. `y` The value plotted with y. ## Discussion ### Discussion Use this initializer to create a horizontal rule across a chart’s plotting area at a y position: ```swift Chart { ForEach(data) { BarMark( x: .value("Department", $0.department), y: .value("Profit", $0.profit) ) } RuleMark(y: .value("Break Even Threshold", 9000)) .foregroundStyle(.red) } ```  See the first code example in [`RuleMark`](/documentation/Charts/RuleMark) for the setup of the structure that contains the `department` and `profit` properties. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)