nested diesel calls in macro

Please help me understand why this macro returns unintended results. The macro is intended to display the difference between to distance entries on the status line. The macro is shown below(with line breaks for clarity) and the screen output with menutrace on. The double quotes around the subtract diesel function do not seem to insulate it from the diesel processor as intended. ARe multiple quotation marks not allowed?

^C^C
dist;\\
setenv;d1;$m=$(getvar,distance);
dist;\\
setenv;d2;"$m=$(getvar,distance)";
setenv;d3;""$m=$(-,$(getenv,d1),$(getenv,d2))"";
modemacro;"$m=$(getenv,d3)";



Command:
Command:
Command: dist
Specify first point: Specify second point:
Distance = 1.000000, Angle in XY Plane = 0.0, Angle from XY Plane = 0.0
Delta X = 1.000000, Delta Y = 0.000000, Delta Z = 0.000000

Command: setenv
Enter variable name: d1
Value <0.5>: Eval: $(GETVAR, distance)
===> 1
Eval: $(-, $(getenv,d1), $(getenv,d2))
Eval: $(GETENV, d1)
===> 0.5
Eval: $(GETENV, d2)
===> 1
===> -0.5
1


Command: dist
Specify first point: Specify second point:
Distance = 0.500000, Angle in XY Plane = 0.0, Angle from XY Plane = 0.0
Delta X = 0.500000, Delta Y = 0.000000, Delta Z = 0.000000

Command: setenv
Enter variable name: d2
Value <1>: Eval: $(GETVAR, distance)
===> 0.5
Eval: $(GETENV, d3)
===> 0.5
0.5


Command: setenv
Enter variable name: d3
Value <0.5>: -0.5


Command: modemacro

Enter new value for MODEMACRO, or . for none <"0">: 0.5