diff --git a/comedi_calibrate/ni.c b/comedi_calibrate/ni.c
index 2f081dd..b9ed8ba 100644
--- a/comedi_calibrate/ni.c
+++ b/comedi_calibrate/ni.c
@@ -117,7 +117,7 @@ static struct board_struct boards[]={
 };
 #define n_boards (sizeof(boards)/sizeof(boards[0]))
 
-static const int ni_num_observables = 18;
+static const int ni_num_observables = 20;
 enum observables{
 	ni_zero_offset_low = 0,
 	ni_zero_offset_high,