Depends.
I find with my system that I need to mash at 2-3 (sometimes 4) degrees Celsius higher than most of the multi-vessel brewers. (I don't think I would want to mash at 78 - I'm assuming a typo there...) Of course, it also depends on your recipe and equipments, etc. I used to try to maintain the exact temperature over the entire duration of the mash, but now I just mash-in a little higher than I think might be about right and let it do it's own thing until I mash-out. I'm much more relaxed than I used to be and I think my beers might be better as a result, which is counter-intuitive to me.
The original guide (found somewhere on AHB) suggests mashing at around 65-66 Celsius for the Schwartzbeer (sp?) the author uses as a first brew. You can't go too far wrong if you follow that and adjust it over a few brews to suit your equipments and taste. But, if you get anywhere between 65 and 70 on your first brew, nothing is likely to happen to make you want to throw the whole thing out, either, in my opinion.
I firmly believe that there are so many factors to brewing that being too prescriptive about too many of them is a mistake. Give it a whirl or twelve and enjoy!

