Slice ginger across the grain as thinly as possible (you'll have about 1 3/4 cups).
Mix with salt.
Cover and refrigerate until next day.
Rinse well and drain.
In a 1- to 2-quart pan, combine vinegar with sugar; bring to a boil, stirring.
Return to a boil, then remove from heat and let cool.
Cover and refrigerate for at least 24 hours or up to 3 weeks.