Measure gin, lime juice and simple syrup into a shaker filled with ice. Here's a convenient measuring jigger that I use. Shake until thoroughly chilled.

Strain into a martini glass. Garnish the glass with a lime wheel.

To make the lime wheel stay on the edge of the glass: Lay the lime wheel flat on a cutting board. Slice into the center of the wheel and move outward, cutting only into the center point of the wheel and moving outward toward the edge—this will create an opening that you can wedge onto the rim of the martini glass.

Sip and enjoy!