a reduction of G. 

constants from Allen 4th ed.

G = 6.672599 e-11  m^3 * kg^-1 * sec^-2
	=> c0 = 6.672599

1pc = 3.0856776 e+16 m 
	=> m^3 = c1 * e-48 pc^3
	=> c1 = 0.0340368

1Msun = 1.9891 e+30 kg
	=> kg^-1 = c2 * e-30 Msun^-1
	=> c2 = 0.50273993

1Myr = 3.15576 e+13 sec
	=> sec^-2 = c3 * e-26 Myr^-2
	=> c3 = 0.316881

G = (c0 * c1) / (c2 * c3) e (-48-11)+(30+26) 
  = 4.5e-3 pc^3 * Msun^-1 * Myr^-2

G^(-0.5) = 15

1pc/1Myr =  0.98 km/sec