diff --git a/example/sim_demo1.py b/example/sim_demo1.py
index 28831f736ff37922e099c684dddafd3cf2b90db9..92d36a0d4734182e07ee2b6d427c58a2a5886509 100644
--- a/example/sim_demo1.py
+++ b/example/sim_demo1.py
@@ -15,7 +15,7 @@ if __name__ == '__main__':
     config = Config(dataDir = dataDir)
     sedFn = dataDir + 'sed/sed_44575.txt'
     psf = galsim.Gaussian(fwhm=0.39)
-    specG = SpecGenerator(sedFn = sedFn, grating = 'GI', beam = 'A', aper = 2.0, xcenter = 5000,ycenter = 5000, p_size = 0.074, psf = psf, skybg = 0.3, dark = 0.02, readout = 5, t = 150, expNum = 1,config = config)
+    specG = SpecGenerator(sedFn = sedFn, grating = 'GI', beam = 'A', aper = 2.0, xcenter = 2000,ycenter = 5000, p_size = 0.074, psf = psf, skybg = 0.3, dark = 0.02, readout = 5, t = 150, expNum = 1,config = config)
     specTab, specImg, img, fluxRa=specG.generateSpec1dforStar()
 
     fits.writeto("specImg.fits",specImg,overwrite=True)