# Quiver. Make wind scale of 1m/s inside plot

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I have had a really tough time thinking of a way to show a scale of the wind vectors that Im plotting.
Im using quiversc(lon,lat,u,v) but I dont know how to put a magnitude of reference (1 m/s for example) , as in the plot below.
Thanks!
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### Accepted Answer

Chunru on 21 Sep 2023
Edited: Chunru on 21 Sep 2023
[x, y] = meshgrid(-2:.2:2);
z = x.*exp(-x.^2-y.^2);
[dx, dy] = gradient(z, 0.2);
sc = 'off'; % scale
quiver(x,y,dx,dy, sc);
axis tight;
hold on
a = axis;
% posision of the ref arrow
xr = a(1)+0.1*(a(2)-a(1));
yr = a(4)-0.1*(a(4)-a(3));
quiver(xr, yr, 1, 0, sc) % unit lenght
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Hi thank you very much! Thanks to your code I manage to do some arrangements, even put the reference arrow to fit more in the plot.
However I have some doubts about it. My code is this one (I use quiversc instead of quiver to control the density of the arrows, but the scaling is the same, I corroborated that):
quiversc(LON,LAT,u*2.5,v*2.5,'off','k','density',60,'LineWidth',1) % off is for scaling
colormap(brewermap(10,'PuBuGn'))
caxis([0 5])
borders('countries','k','LineWidth',1)
borders('countries','k','LineWidth',1)
axis equal
ylim([-30 36])
xlim([30 178])
yticks(-30:30:30)
yticklabels({'30°S','EQ','30°N'})
xticks(40:40:160)
xticklabels({'40°E','80°E','120°E','160°E'})
hold on
a = axis;
xr = a(1)+0.1*(a(2)-a(1));
yr = a(4)-0.1*(a(4)-a(3));
hold on
b = rectangle('Position',[xr-15 yr-6 15 12],'FaceColor','white');
hold on
quiver(xr-13,yr,1*12.5,0,'k','LineWidth',1,'MaxHeadSize',2.5)
The resulting plot is:
So my question is this: I put the manual_sc = 2.5 for the u,v values. Then, to show the reference arrow, I multiply it per 12.5. I understand that, if the whole quiver plot is adjusted with 2.5 and the reference arrow is adjusted with 12.5, then the reference arrow has a magnitude of 4 m/s? I thought about it cause its 4 times bigger than the main quiver plot vectors.
Hey I managed to realize that my question is resolved! I saw the measure of the reference arrow and its indeed the quantity I determined. Thank you so much for your answer, you helped me a lot to improve my plots and to give them a better style
I let my code available for the future if someone has a similar problem

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