Update Progress Counter on Control Field

I’m importing and inserting records into an SQLite table.
I have a PHP variable, $rec_counter, which increments with each record inserted into the table.
An echo statement at the end shows me the $rec_counter variable is being incremented properly.
I also have a integer Control Field defined as, Counter.
During the process I tried updating the Control field, Counter, with this code:
{Counter}=$rec_counter; //That didn’t work.
Then in the Control field definition area, I added Variable Name, counter2, as a session variable and used this code.
{counter2}=$rec_counter; //That did work either.

So… probably just some simple newbie oversight.
How do I get the Control field to update as a progress counter?