If the absolute value of the number to be written exceeds a predefined maximum a conversion is not attempted, but the number is written as a real number in Fortran 'exponential' format and a couple of question marks are appended to its end. This prevents silly results when very large numbers are input. The variable UNITS controls the maximum permitted value for the conversion to be carried out.
The value is written into the part of the string beginning at position IPOSN+1 and IPOSN is returned updated to the position of the end of the encoded angle in STRING.