diff --git a/web/timeline/viewstate.ts b/web/timeline/viewstate.ts
--- a/web/timeline/viewstate.ts
+++ b/web/timeline/viewstate.ts
@@ -1,6 +1,9 @@
-import * as ko from "knockout";
 import * as d3 from "d3";
 import debug from "debug";
+import * as ko from "knockout";
+
+import Sylvester from "sylvester";
+const $V = Sylvester.Vector.create;
 
 const log = debug("viewstate");
 export class ViewState {