I've somewhat recently discovered hyperreal numbers, but I haven't gotten the chance to thoroughly research them.
What resources do you all recommend for undergrad level study of the hyperreal number line and hyperreal numbers? The "undergrad" criterion includes resources that cover hyperreals from both an undergrad and postgrad level. Please note that I wish to learn both the infinitesimals and hyperreal infinities (as opposed to Cantor's transfinites, the infinity on the Riemann sphere, and any other types of infinities), so resources only concerning infinitesimal calculus do not suffice.
Thanks.