If you are using a released version of Kubernetes, you should refer to the docs that go with that version.
The latest release of this document can be found [here](http://releases.k8s.io/release-1.2/docs/user-guide/horizontal-pod-autoscaler.md).Documentation for other releases can be found at releases.k8s.io.
This file has moved to: http://kubernetes.github.io/docs/user-guide/horizontal-pod-autoscaler/