How to have 3 checkboxes when checked, check a fourth text box

[Dave B]

I need the javascript code that would allow me to have a check box (box1) to be automatically checked, when three check boxes (box2, box3, box4) are all checked. If one of the three check boxes are unchecked, then check box (box1) becomes unchecked as well.

Also, check box1 cannot be unchecked or checked manually. 

Hopefully that makes sense.

Thanks,

Dave

[try67]

Create a (hidden) text field with the following custom calculation script:

var a = this.getField("box2").valueAsString!="Off";
var b = this.getField("box3").valueAsString!="Off";
var c = this.getField("box4").valueAsString!="Off";
this.getField("box1").checkThisBox(0, a && b && c);