The E-530 marked a big advance in the E-series meters. It has 5 ranges, from X.01 to X100. This latter is used only with a provided internal energy compensated GM tube, and is scaled for 0-2000 mR/h. Simple layout, good quality components.......Victoreen regulator tube, excellent quality switches, extra robust ( thick) glass epoxy circuit boards make the E-530 a real winner. Input sensitivity is set to 12 mV fixed, but each of the 5 ranges has it's own cal pot. For a quarter century old design, it is right there with the best of today's offerings. An extra folding clip on the closure hardware provides an attachment point for a carry strap, not evident in later models.
These are typically set up to use with an energy compensated GM such as the Eberline HP-270.
The E-530N is the same meter with "enhanced" ability to contend with moist conditions (basically a gasket on the cannister).