Rifle Scopes Which Holland level?

Re: Which Holland level?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jackalope33B</div><div class="ubbcode-body">get the one that mounts to your scope. just incase your rail is off slightly, you can always adjust the scope mounted version so it is level </div></div>

Thank you. That leads to another question- how do you install/calibrate these? Thanks