Selected Answer
It does make sense - but not enough.
Depending upon what you want to look up and where, you would probably use VBA's Find function to retrieve the data. Basically, you would replicate VLOOKUP, looking for the date in one column and returning the value from another column in the same row (works for HLOOKUP in analog fashion). You wouldn't use VLOOKUP because you need to replicate the search when you want to update the cell in reverse.
Find returns a range, in this case a single cell, the value of which you can read and use or set. Use the worksheet's Change event to trigger the update.
In the attached workbook I have reviewed your code and formatted it for better readability. I didn't test it, nor checked its logic but I corrected and improved the syntax and added some comments for your reading pleasure.
If you wish to pursue your original question in this thread please don't explain what you want in any comments - edit your question so that it provides the required information. My feeling is that you should first try to implement the answer I provided here and post any questions that probably arise in a new thread when you come to them.