This is a Tower Hobbies Digital LCD Mini Tachometer. This Digital Mini-Tach is the perfect addition to any flier"s Field Box. The Digital Mini-Tach allows you to accurately monitor engine performance and evaluate the effects of different fuel and props to improve your model"s performance. FEATURES: Durable ergonomically-designed, durable black case with rubber bumper strip increases ease of use and durability. Includes two pre-installed "AAA" batteries Auto-OFF after 5 minutes, if not in use. One-touch switch operation with a protective ring that prevents accidentally switching the unit ON in the Field Box Operating range 0-32,000 RPM Measures 2-, and 3- Bladed props Can be used up to 12" away from propeller Large easy-to-read .5" (13mm) LCD display One Year Limited Warranty through Hobby Services beginning at date of purchase INCLUDES: One LCD Digital Mini-Tachometer REQUIRES: Nothing, AAA batteries are included. SPECS: Length: 3¾" Width: 2½" COMMENTS: Hold tach 4" to 12" away from propeller. Uses 2 "AAA" alkaline batteries for replacement when necessary. This Tachometer uses a sensitive photocell to measure the number of times the propeller blade crosses between the sensor and the light from the sun. If the readings become erratic, change the direction the model is facing by 90° and take another reading. Do not use indoors, reading will not be accurate. Instructions are printed on the box. JAL 2/23/00 ir/jl updt jxs 05/21/10