The road block is more a description of the termination of the code with the while loop followed by the double empty braces - no further values appearing on the serial monitor and no call to pin 15 to spark life back into the sketch. And having read about the flexible for loop in the reference section I figured it could also do this job - but I forgot to put in all the semicolons like so for(1==1;;){} and that does seem to do the same job. Anyhow a diversion. I'm still working on the nesting for loops and additional arrays and variables (all at once)...