Sometimes you might want to get the Text Value of a Select Dynamic Field. This can be accomplished by using some script in the Script (JS) field when you edit the Select Dynamic Field. Click the blue down arrow under the Storage to open the Stuff section and find the Script(JS) section. 

Then you can use the following:

document.getElementById("My_Dynamic_Field").onchange= function() {myFunction()};

function myFunction(){
var dd = document.getElementById('My_Dynamic_Field');
idToFind = dd.value;

textToFind = dd.options[i].text;

document.getElementById("My_Text_Field").value= textToFind;