derived from the observations (see Section \[cloudshocks\], below) is $P_{\mathrm{ram}} = 3.3\times10^{-7}$dynes/cm$^2$. At the mean pre-shock particle density implied for these shocks, $n_0 \sim 240$cm$^{-3}$, the mean cooling age to $T_e = 1000$K is 400yr. This provides an initial estimate of the shock age. Another way is to take the age of the SNR as estimated from the \[\] dynamics of the fast-moving material and estimate from the position of the cloud within the SNR how long it has been since the blast wave overran the cloud. In Section \[intro\] we saw that estimates of the age of N132D vary from 1350 – 3440yr for the SNR, with a probable age of $\sim 2500$yr [@Danziger76; @Lasker80; @Vogt11]. The detailed position of the clouds within the SNR blast wave cannot be reliably estimated from their projected distances from the boundary of the shell, but we will take this as being $\sim 25$%, as an upper limit, giving a mean shock age of $\lesssim 600$yr.

With the shock ram pressure given above, the mean pre-shock density at a given shock velocity is fully determined; for shock velocities of 300, 350 and 400km/s the pre-shock particle densities are 160, 117 and 90cm$^{-3}$, respectively. 