! Cursor w/ ruler line - Toggle

cursorRulerLine.js

javascript : (function () {
   if (!document.getElementById("redLine")) {
      h = document.createElement("div");
      h.setAttribute("id", "redLine");
      h.setAttribute("style", "width:100%;height:3px;background-color:red;font-size:inherit;line-height:inherit;position:absolute;left:0px;top:0px;z-index:999;opacity:1;");
      document.getElementsByTagName("body")[0].appendChild(h);
      window.onmousemove = function (e) {
         var h = document.getElementById("redLine");
         h.style.top = (e.pageY + 15) + "px";
         h.setAttribute("class", e.pageY);
      }
   } else {
      h.remove();
   }
})();

// Bookmarklet
// Adapted from https://gist.github.com/bradmontgomery/1787016