I have the same problem. I'm using Xor.hdl as a test. After loading the Xor.hdl, and changing the inputs (a and b), the calculator icon is (still) not available.
I also tried running the corresponding test script Xor.tst, and it fails at line 3.
I can add that I've tried using both Windows 10 and Linux Mint 20. On Linux, I'm using the following version of Java:
openjdk 11.0.14.1 2022-02-08
OpenJDK Runtime Environment (build 11.0.14.1+1-Ubuntu-0ubuntu1.20.04)
OpenJDK 64-Bit Server VM (build 11.0.14.1+1-Ubuntu-0ubuntu1.20.04, mixed mode, sharing)
I'm using the file nand2tetris.zip downloaded from the website. It has a size of 731739 bytes and an md5sum of 592f4146796d204e022b151ff8eb6c13
The screen shot is:
![](http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/file/n4036761/Screenshot_from_2022-04-10_13-31-16.png)
The Xor.hdl file I'm using is:
// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/01/Xor.hdl
/**
* Exclusive-or gate:
* out = not (a == b)
*/
CHIP Xor {
IN a, b;
OUT out;
PARTS:
Not (in=a, out=nota);
Not (in=b, out=notb);
And (a=a, b=notb, out=aAndNotb);
And (a=nota, b=b, out=notaAndb);
Or (a=aAndNotb, b=notaAndb, out=out);
}