I have seen this question in CRM development forum, where user asked how to set ‘Default Unit’ using javascript, so I wrote below function to do the same

function SetDefaultUnit()

{

if(Xrm.Page.ui.getFormType() == 1) //Check form type

{

var number = 1;
var filter = “/UoMScheduleSet?$select=Name,UoMScheduleId&$filter=Name eq ‘Default Unit’”;   //Make sure you have created ‘Default Unit’ record
RetrieveUnit(filter);
}

}
function GetODataPath() {

return Xrm.Page.context.getServerUrl() + “/xrmservices/2011/organizationdata.svc”;
}
function RetrieveUnit(filter) {

var retrieveRecordsReq = new XMLHttpRequest();
retrieveRecordsReq.open(“GET”, GetODataPath() + filter, false);
retrieveRecordsReq.setRequestHeader(“Accept”, “application/json”);
retrieveRecordsReq.setRequestHeader(“Content-Type”, “application/json; charset=utf-8”);
var temp= retrieveRecordsReq.send();

//check status
if (retrieveRecordsReq.readyState == 4 && retrieveRecordsReq.status == 200) {
var retrievedRecords = this.parent.JSON.parse(retrieveRecordsReq.responseText).d;
var Result = retrievedRecords.results[0];

//Set lookup
var lookup = new Object();
var lookupValue = new Array();
lookup.id = Result.UoMScheduleId;
lookup.entityType = “uomschedule”;
lookup.name = Result.Name;
lookupValue[0] = lookup;
Xrm.Page.getAttribute(“defaultuomscheduleid”).setValue(lookupValue);
}
}

Just create a webresource and attach that webresource to product form and call SetDefaultUnit function onload of product form.

Hope it will help somebody !!