Oh...My friends.
I will tell you How do Rangefinder working ? Because i am professionally.... LOL...
Rangefinder also called. Rangefinder Binocular or Monocular. always got optical design like 4x 6x 7x etc... Magnifications. that is view system, like Binoculars. you can uses your eyes view from one said. and this product got LCD display and Aim cirles inside that your eyes can see it. when you found any object like tree. house. people. dog. flag. any you want to measure distance just move the center aim circle on them. and push the power button then the distance between rangefinder and object will come out under 1 seconds. very quickly. and also rangefinder got many different working models. Scan. Automatically Measuring. no need any operations. and Flag Pinseeker models. specially for golfers. and hunting model. etc...
the principle for rangefinder is this product got laser diode design inside. but here you need to read carefully. cause Laser it.s means not safety for peoples eyes. that.s why you choice one rangefinder you need to see if they got any FDA or IEC safty certifications or symbol. aftery got such certifications eye safty. but you can not aim to the sun directly that will burn your eyes. when you push the power button. the laser diode will emitting many laser pulses..to the object and when those pulses comes with the object will back to rangefinders (got receives) then account the times of laser coming and back. then got the distances. the accuracy always will be like in 1 meter.
Like people said. not easy to aim the pin. cause it.s too crazy thin...but some rangefinder can measure distance to pin in 100-150meters. but most golfer aim golf flag can reach 300meters.
I hope this will help you know how rangefinder workes ? if you got any concusious. feel free to contact with me. haha.
GPS uses satelite. can see maps. but the accuracy not good. and also can not uses for other outdoor uses. cause rangefinder can also be used for binoculars and monaculars for climbing or any you want in outdoor uses too. and those two kind price got almost same prices. i wish you can choices rangefinders if you want to buy some. but it.s just my personnel suggestions.