There's no need to sugarcoat it—the needle is tough to move at the NBA combine.
Day 1 consists of drills that test simple fundamentals. The players are separated into groups by position where they're drilled on skills that correlate with their projected future responsibilities.
Coaches and general managers are using the eye test here—who stands out physically, who looks fluid, whose jumper is likely to translate.
You can't take much away from the drilling portion of the combine except who looks comfortable in each facet of the game. Here are some observations from Day 1 at the combine with regard to what scouts saw and how they likely viewed it.