Selecting Last Entered Value as Lookup

Selecting Last Entered Value as Lookup

Sorry if this is a basic question, I'm a noobie to Zoho. To simplify-

I have a Form1 that has the fields, Date and Weight
On My Mainform, I want to populate a "Current Weight" field with the last Weight that was entered  on Form1 (Which should correspond to the record with the most recent Date,)

How can I do this? I can have a dropdown box appear with Date and Weight displayed for the user to manually select the last one, but how to automatically populate the "Current Weight" field ?

What is the Deluge to do this? I can think of ugly ways to get this done (global variable- i.e. store the latest Weight value in a third form.) but there must be a more elegant way.

Thanks