From three devices at the same time can not receive a accurate signal?

Archive
1

Distance units are cm.
beacon A : (0,0)
beacon B : (500,0)
beacon C : (0,500)

iPhone(0,250)

iPhone received distance from A : 240
B : 280
C: 340

From three devices at the same time can not receive a accurate signal?

2

Could you please try setting power to a higher level?

https://estimote.zendesk.com/hc/en-us/articles/201098688-How-to-change-the-range-of-a-beacon-

Let me know, if that has helped.

3

Android devices I can get a relatively stable value.
However, to get the value of the iPhone device unstable.

4

Check out the video that has been recently released by Apple: https://dl.dropboxusercontent.com/u/1071328/ibeacon-apple-techtalk.mov

It explains what happens with all Apple devices, so I hope it helps. If not, please get back to us.

5

It means iOS and Android deal with beacons in a different way, and they have different hardware as well. In the end of the day, BLE is not always precise and stable. Even GPS is not.
A simple microwave oven or a nearby cordless phone can mess up the "stability" that you my want to have. That's why Apple calls CLLocation's property "desiredAccurracy" the way it is.
It applies to all devices using wireless transmission, WiFi, you name it.