How to keep a calculation field blank until the user enters a number?

Question

I am building a sales sheet for a school that sells scrip as a fund-raiser. I have the document set so that when the user enters the number of scrip certificates he wants (say, two $25 gift certificates at Lowe's), the program will automatically calculate that this user owes $50 for that scrip category. However, there are more than 100 companies that one can choose from, and if the user doesn't enter a number, the calculated field shows $0. Is there a way that each field can stay blank until the user enters a number bigger than zero? By the way, I'm using this calculation to determine the value (borrowed from a user on this forum): event.value = 50 * this.getField("Lowes").value
Thanks!

Answer 1

There are two approaches. You can either add the following Validate script:
// Custom Validate script for calculated field
if (+event.value !== 0) event.value = "";
Or you can change your custom Calculate script and set the Format type of the field to "None":
// Custom Calculate script
(function () {
    var v = +getField("Lowes").value;
    event.value = (v !== 0) ? util.printf("$%.2f", v) : "";