diff --git a/pub/src/curve.cpp b/pub/src/curve.cpp
index 3c7108502d88cd9e3293031bca3e378603974002..6477ce93ecc382857552d14ae983cb2496436df9 100644
--- a/pub/src/curve.cpp
+++ b/pub/src/curve.cpp
@@ -107,9 +107,28 @@ ask_again:
         "    c: external curve evaluation command (hc for help)\n"\
         "    ci: external command followed by interpolation (hci for help)\n";
         goto ask_again;
+    } else if ( expr=="hc" ) {
+        cout <<
+            "the external curve evaluation command must:\n"\
+            "- read from stdin a whitespace separated list of:\n"\
+            "  - 1*int:    the number of parameters M\n"\
+            "  - M*double: the parameters\n"\
+            "  - 1*int:    the number of data points N\n"\
+            "  - N*double: the data points\n"\
+            "- write to stdout a whitespace separated list of:\n"\
+            "  - N*double: the curve values\n";
+        // "for examples, see /usr/local/share/frida/demo-curve-c"
+    } else if ( expr=="hci" ) {
+        cout <<
+            "the external curve evaluation command must:\n"\
+            "- read from stdin a whitespace separated list of:\n"\
+            "  - 1*int:      the number of parameters M\n"\
+            "  - M*double:   the parameters\n"\
+            "- write to stdout a whitespace separated list of:\n"\
+            "  - 1*int:      the number of data pairs N\n"\
+            "  - N*2*double: a sequence of data pairs: x0 y0 x1 y1 x2 y2 ...\n";
     } else if ( expr=="c" ) {
         evaMode = COlc::_SCR;
-        throw "not yet implemented";
         expr = sask( "Curve evaluation command ?" );
         np = iask( "Number of parameters ?" );
     } else if ( expr=="ci" ) {
@@ -149,7 +168,28 @@ void COlc::curve_val_vec( vector<double>* ret, const vector<double>& vt,
                 throw "BUG: tree_curve_val did not get vectorial result";
             *ret = val.v;
         }
-    } else if ( evaMode==_SCR_INTP ) {
+    } else if ( evaMode==_SCR || evaMode==_SCR_INTP ) {
+
+        string par_fifo = string("/tmp/par-") + getenv( "LOGNAME" );
+
+        mystd::system( "rm -f "+par_fifo );
+        if (mkfifo( par_fifo.c_str(), 0666 ))
+            throw "SYSTEM ERROR cannot make fifo " + par_fifo +
+                " needed for external curve call";
+
+/*
+    mystd::system( "gnuplot -title " + strg(iPlot) + " -noraise" +
+                   " < " + par_fifo + " &" );
+
+    // we use open instead of fopen or ofstream,
+    // because we need non-blocking mode.
+    if (!(gp_fifo = open(par_fifo.c_str(), O_WRONLY)))
+        throw "SYSTEM ERROR cannot open fifo " + par_fifo +
+            ": will not be able to print";
+    fcntl(gp_fifo,F_SETFL,O_NONBLOCK);
+
+    gp_write( string("set terminal x11") );
+*/
         FILE *F;
         if( !(F = fopen("/ram/pars", "w")) )
             throw "BUG: cannot write system call pars";
diff --git a/pub/src/dualplot.cpp b/pub/src/dualplot.cpp
index 94169823c7670c1825556a1fcf88bf04100bce4d..82dddf04aa5a1a6c6583a9be283c5fbde38753b9 100644
--- a/pub/src/dualplot.cpp
+++ b/pub/src/dualplot.cpp
@@ -32,7 +32,7 @@ CPlot::CPlot( uint _iPlot, bool _logx, bool _logy ) :
 
     mystd::system( "rm -f "+fn_fifo );
     if (mkfifo( fn_fifo.c_str(), 0666 ))
-        throw "SEVERE SYSTEM ERROR cannot make fifo " + fn_fifo +
+        throw "SYSTEM ERROR cannot make fifo " + fn_fifo +
             ": will not be able to print";
 
     mystd::system( "gnuplot -title " + strg(iPlot) + " -noraise" +
@@ -41,7 +41,7 @@ CPlot::CPlot( uint _iPlot, bool _logx, bool _logy ) :
     // we use open instead of fopen or ofstream,
     // because we need non-blocking mode.
     if (!(gp_fifo = open(fn_fifo.c_str(), O_WRONLY)))
-        throw "SEVERE SYSTEM ERROR cannot open fifo " + fn_fifo +
+        throw "SYSTEM ERROR cannot open fifo " + fn_fifo +
             ": will not be able to print";
     fcntl(gp_fifo,F_SETFL,O_NONBLOCK);