Using
alpha4.printFloat(stack[1], 2, 10)
I get the error message
'class Adafruit_AlphaNum4' has no member named 'printFloat'
However println works for integers
alpha4.println(counter);
BUT unfortunately the segment digits do not fully map from 7-segment to 14-segment.
The centre bar is split on the 14 segment display and half of it lights up, the other half lights up instead if the decimal point!
Anyway printFloat() does not really make sense when limited to a 4 digit display and something much more sophisticated is needed to run the conversion over 4 objects each with 4 digits.
I will take the library code for printFloat() and see if I can reuse it. Unless someone comes up with a C++ library function.
Thanks for your help.