You did not copy the formula correctly. It is:
Acc << New Column( "lo50%expGMT", Numeric, Continuous, Formula(If(round(:expGMT / 2 ) >= 10,round(:expGMT / 2 ), 5)));
Please review the structure of an IF() clause in the Scripting Guide
Help==>Books==>Scripting Guide
There are 3 sections to an IF() clause.
If( comparison, what to do if the comparision is true, what to do if the comparison is not true);
Therefore:
If( round(:expGMT / 2 ) >= 10 // The comparision
,round(:expGMT / 2 ) // What to do if true
, 5 // what to do if not true
)));
Jim