I don't know how to do it with an annotation, but here is a way to do it with the text() function, using the XLim and YLim properties of the plots (without needing to know the ranges of the x and y data beforehand):
figure
plot(1:10)
xlim=get(gca,'XLim');
ylim=get(gca,'YLim');
ht = text(0.5*xlim(1)+0.5*xlim(2),0.6*ylim(1)+0.4*ylim(2),'My text');
set(ht,'Rotation',45)
set(ht,'FontSize',18)
In the text command, make sure that the fractions add up to 1 for both the x and y positions, and then it is easy to steer the text to where you want it, and make it consistent across figures.
Best Answer