Print followed by parenthesis is interpreted as you passing a channel number. That means the first part of your formula (2/6374) is evaluated to zero. So the remainder of the print ‘-(1/6557.5)’ is output to screen.
You can fix this by putting a 0+ in front of the formula:
->? 0+(2/6374)-(1/6557.5)
.1612775690797811975E-03