Why is triangle the wrong size?

I am trying to draw a simple equilateral triangle with the Draw Polygon tool. I followed thesde steps:

1. Click the Draw Polygon button, enter the drawing area.
2. Click to mark the center, and drag to begin drawing a hexagon.
3. Rease the mouse button and press Space to enter the size field.
4. Type 0.05 into the size field and press Tab to move to the angle field.
5. Type 0.0 into the angle field and press Tab tomove to the sides field.
6. Type 3 into the sides field, and shape changes from a hexagon to a triangle, and numbers in all fields are correct.
7. Tab out of the sides field, then press Enter to confirm that's what I want.
8. Click the Mode button, and return to the normal drawing area with the triangle in place.
9. Select the Measure tool and click one side of the triangle. The Measure tool says the length of the side is 0.0866"!!

What the heck is going on? Nothing in the triangle should be larger than 0.05", and thebase-to-apex should be 0.043". Am I doing something wrong?

Thanks.