Ah foxmoth! Now I see where grand total comes into it. My logbook does not have this but merely has a "total time" column which is added at the bottom.
I also agree with the last posts about logging electronically. I personally keep a paper logbook as well but it's so so much easier to keep whenever I fill it in from an e-logbook that has done all the calculations for me. I have used so much less tipex since I started doing it this way (unfortunately it still is occasionally used whenever I fail to engage my brain before putting pen to paper).