An ideal Ammeter has zero internal resistance so if you connect it in parallel with an ideal voltage source - which has zero source resistance - it will pass an infinite current. In EasyEDA, the default voltage sources are ideal but the Ammeter has an internal resistance of 1mOhm so when you connect it across a 5V source it will draw, and therefore indicate, 5000A. If you short the terminals of an ammeter having a non-zero internal resistance with an ideal wire having zero resistance then all the current in the wire will pass though the wire and none will flow through the Ammeter so the Ammeter will show 0A. It may help you to read the Simulation Tutorial (3) in (2) in: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a)<br> <br> since this sort of misunderstanding is largely explained in the early part of it under: **Introduction to using a simulator > Avoiding common mistakes.**