This came from http://www.usachoice.net/post-32/flagetiq.html

The Flag in Mourning
To place the flag at half staff, hoist it to the peak for an instant and lower it to a position half way between the top and bottom of the staff. The flag is to be raised again to the peak for a moment before it is lowered. On Memorial Day the flag is displayed at half staff until noon and at full staff from noon to sunset.

The flag is to be flown at half staff in mourning for designated, principal government leaders and upon presidential or gubernatorial order.

When used to cover a casket, the flag should be placed with the union at the head and over the left shoulder. It should not be lowered into the grave

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Another site I read indicated that half-mast and half-staff are one and the same, and that half-masting flags on private residences is up to the discretion of the owner. I guess you can always take your cue from governmental buildings (?).