Ohaus hb4al dry block heater, 4 block, analog, 120v versatile dry block heaters are ideal for applications that require temperature stability. All units hold 2 optional interchangeable modular blocks with over 40 choices. Blocks are easy to use, no tools required. Close tube-to-block contact enables maximum heat retention, resulting in efficient heating. Digital models offer exceptional temperature uniformity and stability for repeatable results, while non-digital models are an economical choice. applications: incubation & activation of cultures, enzyme reactions, immunoassays, melting/boiling points, isothermal incubations, nucleic acid denaturation display: led display (digital models) and dual-adjustment knobs with dial markings (analog models) operation: detachable 3-wire cord and plug (included), analog models require an external thermometer or temperature device for temperature setpoint construction: painted steel housing, support rod holder with locking knob design features: touchpad control and audible alarm (digital models)