I created open end question for such type of problem and used custom javascript to check if it consists numeric value only, In my case, I created grid question S9b and used below script to check this.
var checkOK = "0123456789";
var k=0;
var check=new Array();
var allValid = true;
var str = document.mainform.S9b_r1_c1.value;
var str1 = parseInt(document.mainform.S9b_r1_c1.value);
for (i = 0; i < str.length; i++)
{
ch = str.charAt(i);
for (j = 0; j < checkOK.length; j++)
if (ch == checkOK.charAt(j))
break;
if (j == checkOK.length)
{
allValid = false;
break;
}
}
if ((!allValid) || (str1==0))
{
strErrorMessage="A response is required.";
}
If you are looking to update any quota based on this value then use below function:
StringToNumber(S9b_r1_c1)
Hope it helps you.