Try Copy column properties from dt1, then past column properties to dt2. When use update table, the formula got lost.
Names default to here(1);
// → Data Table( "Big Class" )
dt1=Open( "$SAMPLE_DATA/Big Class.jmp" );
// Launch platform: Bivariate
Biv= dt1<<Bivariate( Y( :weight ), X( :height ), Fit Line(1) );
Biv << (Curve["Linear Fit"] << Save Predicteds);
dt2 = New Table( "New ht",
New Column( "height", numeric, continuous, set values([59,75]) ),
New Column( "weight", numeric, continuous ),
);
dt1 << Copy Column Properties ({:Predicted weight});
dt2 << Paste Column Properties ({: weight});
// Update data tables lose formula
dt2 << Update(
With( dt1 ),
Match Columns( :height = :height ),
Add Columns from Update Table( :Predicted weight ),
Replace Columns in Main Table( None )
);