You will remember our snow splitter. It collapsed under the onslaught of a thaw plus a lot of snow on the roof. If you don't remember, the relevant tag is "splitter."
So we are rebuilding the splitter. This time we used batter boards.

 A batter board is a simple framework upon which strings are set up. You adjust the strings so as to have equal diagonals. It is much easier to adjust strings than to adjust big heavy posts. You try to keep the string square, but the ultimate test is the diagonals. This is used both by constructors of big heavy structures and by cabinetmakers. If your diagonals are equal, the strucure is square, and that gets you out of a great many difficulties, because in construction you cannot rely on carpenter's squares, and the same is true for cabinetmakers. You should level the strings. I used a line level for the purpose. Then I sawed a notch in the batter board so that I wouldn't lose the reference.  Now you have corners for your framework. You dig holes at those corners.

Then (much later, like today) we set up the posts. Below, Fluffy holds up a post prior to leveling. John has rigged supports so we can plumb the posts.

 Once you have the batter boards (and the strings) it is relatively easy to set up the posts. Note that we have encased the posts in plastic bags. A bit of insurance against moisture seeping in.  We thank Fluffy's father for the advice. The posts are supported by temporary braces. Thanks, John.

And the rest is pouring concrete. So we did. A bag of concrete, high-early-strength (HES) stuff does the trick. One bag per upright post, but just in case we will add some more concrete. Lowe's is your friend. In the picture above Fluffy and John are recycling our concrete bags to provide a tent for our concrete, in case it rains tonight. It probably will. This is Alaska. Fall is rainy.  It has rained continually for the last week. This one day, it did not rain, and  we got a lot done. The posts are plumb . We will pour some more concrete as insurance, but this is a major step forward.