Something changed in my spreadsheet and when I enter a formula (=INDEX(xxx, MATCH(yy,zz,0))), it is considered a constant. By that I mean, it thinks it is a regular text string. I tried several experiments to diagnose the problem. I added columns to the table with the same result. I added a new table in a new tab with the same result. Existing cells work fine. When I add a row to the table, the formulas from the other rows in the same column work fine. I must have inadvertantly set a parameter which is causing this but I can't find it. I also made sure the calculation mode is on "Automatic" but this shouldn't be the problem even it it was on.