Temporal (left panel) and spatial (right panel) variation of helium isotopic ratio in the solar neighborhood and along the galactic disk at the present time, respectively. Models are the same as in Fig. 7. Data are from Geiss & Gloeckler (1998) for the PSC (green filled circle), Bania et al. (2002) for Galactic HII regions (black dots), and Gloeckler & Geiss (1996) for the LISM (orange filled trangle). 1-σ and 3-σ errors are also shown as thick and thin lines, respectively.