diff --git a/run_syncmd.py b/run_syncmd.py
index 6d2a922..6b56d39 100644
--- a/run_syncmd.py
+++ b/run_syncmd.py
@@ -111,7 +111,7 @@ def make_specgrid(specfile='syncmd_spec.grid.hd5',
 def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
                  specfile='syncmd_spec.grid.hd5',
                  astfile='ast_half1+3_wbg.fits',
-                 av_fg=0.18, av_red_mean=0.4, av_red_loc=0.0, av_red_sig=0.55,
+                 av_fg=0.18, av_red_median=0.4, av_red_loc=0.0, av_red_sig=0.55,
                  av_unred_max=0.0, dmod_sig_old=0.15, dust_dmod_relative=-0.1,
                  sclh_ratio_max=10., sclh_ratio_min=1.,sclh_loga_transition=8.5,
                  useF99dust=False,
@@ -121,6 +121,12 @@ def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
     Create SED grid from spectral grid, applying dust attenuation and
     distance shifts.  Write output SEDs into a FITS file.
 
+    Model includes age-dependent extinction, implemented as a simple two
+    component model (young stars, old stars; divided at age defined by
+    sclh_loga_transition) where variables are linked:
+    1) dmod_sig_old sets maximum DM, 2) dmod_sig_dust set by dmod_sig_old &
+    sclh_ratio_max, 3) dmod_sig_yng set by dmod_sig_dust & sclh_ratio_min
+
     Parameters
     ----------
 
@@ -135,8 +141,9 @@ def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
         input file for ASTs; format = .fits
     av_fg: float
         foreground (MW) Av in magnitudes; default = 0.1 mag
-    av_red_mean: float
-        mean of lognormal dist. for Av in magnitudes; default = 0.5 mag
+    av_red_median: float
+        median of lognormal dist. for Av in magnitudes; where
+        av_red_mean = av_red_median * exp(av_red_sig**2./2.0); default = 0.5 mag
     av_red_loc: floag
         zeropoint of lognormal dist.; default = 0.0 mag
     av_red_sig: float
@@ -152,9 +159,15 @@ def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
         offset of dust from average distance, given in mag w.r.t. average
         distance modulus; default=-0.05 mag
 
-    sclh_ratio_max = 10.
-    sclh_ratio_min = 1.
-    sclh_loga_transition = 8.5
+    sclh_ratio_max: float
+        for step-function scale height model, this is large value adopted at
+        old ages when dust is in thin plane with respect to dust; default = 10.
+    sclh_ratio_min: float
+        for step function scale height model, this is small value adopted at
+        young ages when stars and dust are well-mixed; default = 1.
+    sclh_loga_transition: float
+        log(age/yr) of step-function transition point for scale height
+        difference; default = 8.5
 
     output_raw_cols: boolean
         flag to add RAW and ORIG columns to output file
@@ -192,12 +205,12 @@ def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
     dmod_offset = (dmod_offset_raw * idmod_sig) + idmod_off
 
     # Set Av Distribution
-    # Current: Lognormal w/ mean=av_red_mean, sigma=av_red_sig
+    # Current: Lognormal w/ median=av_red_median, sigma=av_red_sig
     #   -Dust Pos = dust_dmod_relative, sets f_red
     #   -Foreground Pop = Uniform from Av=0-av_unred_max
     #   -MW Foreground = av_fg added to all sources
     av_draw = scipy.stats.lognorm.rvs(av_red_sig,loc=av_red_loc,
-                                      scale=av_red_mean,size=N)
+                                      scale=av_red_median,size=N)
     #av[np.where(av < 0.0)] = 0.0 #Clip negative Av tail
 
     # Assign Av via Z distribution
@@ -273,12 +286,14 @@ def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
     g = SpectralGrid(_lamb, seds=_seds, grid=Table(cols), backend='memory')
     g.grid.header['filters'] = ' '.join(filters)
     g.grid.header['av_fg'] = av_fg
-    g.grid.header['av_red_mean'] = av_red_mean
+    g.grid.header['av_red_median'] = av_red_median
     g.grid.header['av_red_loc'] = av_red_loc
     g.grid.header['av_red_sig'] = av_red_sig
     g.grid.header['av_unred_max'] = av_unred_max
     g.grid.header['dmod'] = distanceModulus
     g.grid.header['dmod_sig_old'] = dmod_sig_old
+    g.grid.header['dmod_sig_yng'] = dmod_sig_yng
+    g.grid.header['sclh_loga_transition'] = sclh_loga_transition
     g.grid.header['dust_dmod_relative'] = dust_dmod_relative
     g.grid.header['f_red'] = f_red
     g.grid.header['extlaw'] = extLaw.name
@@ -372,11 +387,13 @@ def make_sedgrid(sedfile='syncmd_sedsobs.fits', sedfilegrid=None,
 
     # Header Info
     data.meta['av_fg'] = av_fg
-    data.meta['av1_mean'] = av_red_mean
+    data.meta['av1_median'] = av_red_median
     data.meta['av1_sig'] = av_red_sig
     data.meta['av0_max'] = av_unred_max
     data.meta['dmod'] = distanceModulus
     data.meta['dmod_sig_old'] = dmod_sig_old
+    data.meta['dmod_sig_yng'] = dmod_sig_old
+    data.meta['sclh_loga_transition'] = sclh_loga_transition
     data.meta['dmod_rel'] = dust_dmod_relative
     data.meta['f_red'] = f_red
     data.meta['extlaw'] = extLaw.name