How to make a proper Gibson?

I have a One Shot glass that can measure .5 oz 1 oz and 1.5 oz and a nice shaker along with Martini and Rossi dry vermouth and I’m about to have Seagrams gin and cocktail onions.

How do I use what I have to make an Ideal Gibson? The recipes I’m finding are for giant 3 oz pours and I’m seeking a recipe that makes a standard 1.5 oz drink.