Trying to do everything exactly the same each time (including the number of agitations) is the key to consistency. Some people claim you'll get better tonality with slower inversions--one every two seconds or so. And, as was already mentioned, ten seconds every minute (or four to five inversions) may give you better sharpness at the expense of a little more grain. Another consideration is that D-76 tends to gain contrast as it ages, and grain usually follows contrast.(posted 8593 days ago)