Database for double data entry

I'm trying to create a database in MS Access set up for double data entry
purposes with input messages, error alerts and automatic formulas for
calculation. It should be such that the second user should not see what the
first user entered unless there is a discrepancy in a certain field. Then
he/she will get an error message and a prompt as to what to do. Does anyone
have any ideas on how to get this done? Thanks in advance for any help.