George - if you want to just update the existing annotation (rather than creating a new one on each iteration of the while loop) then you need to store the handle to the annotation and then use it for the update. For example,
hAnnotation = annotation('textbox',[0.75, 0.1, 0.1, 0.1],'string', "");
hold on;
while (toc<30) %Loop when Plot is Active will run until plot is closed
vx=readVoltage(a,'A0');
vy=readVoltage(a,'A1');
%.........
steps = stepleftacc + steprightacc
set(plotGraph,'XData',time,'YData',data);
axis([0 time(count) -90 90]);
pause(delay);
set(hAnnotation, 'String', "steps:" + steps);
% etc.
end
We create the annotaiton object outside of the loop and then update it on each iteration.
