adding a new scale to drop down list

When in paper space right-clicking on the viewport one gets a drop down of preset scales. I need to print a drawing at a scale that is not listed in the drop down, could anyone help with how i go about adding a new scale? for eg there's 1/8"=1'0 and 1/6"=1'0" but i need a scale of 1/10"=1'0 . how doI set that up and add it the the drop down list Thanks for responses