diff --git a/libeos/call_string.py b/libeos/call_string.py
new file mode 100644
index 0000000..9433128
--- /dev/null
+++ b/libeos/call_string.py
@@ -0,0 +1,79 @@
+# module to assemble an orso 'call' string form command line arguments and some default values.
+
+def call_string():
+    base = 'python eos.py '
+
+    inpt = ''
+    if clas.year:
+        inpt += f' --year {clas.year}'
+    else:
+        inpt += f' --year {datetime.now().year}'
+    if clas.dataPath:
+        inpt += f' --dataPath {clas.dataPath}'
+    if clas.subtract:
+        inpt += f' -subtract {clas.subtract}'
+    if clas.normalisationFileIdentifier:
+        inpt += f' -r {clas.normalisationFileIdentifier}'
+    # get file list somehow
+    if ...:
+        inpt += f' -n {flie_list}'
+    else:
+        inpt += f' -n {clas.fileIdentifier}'
+
+    otpt = ''
+    if outputFormats != 'Rqz.ort':
+        otpt =  f" -of  '{outputFormats}'"
+    if clas.outputName:
+        otpt += f' -o {clas.outputName}'
+    else:
+        pass
+        # default name
+        
+    mask = ''    
+    if clas.yRange:
+        mask += f' -y {clas.yRange}'
+    if clas.lambdaRange:
+        mask += f' -l {clas.lambdaRange}'
+    if clas.thetaRange:
+        mask += f' -- thetaRange {clas.thetaRange}'
+    elif clas.thetaRangeR:
+        mask += f' -t {clas.thetaRangeR}'
+    if clas.qzRange:
+        mask += f' -q {clas.qzRange}'
+    if clas.qResolution:
+        mask += f' -a {clas.qResolution}'
+
+    para = ''
+    if clas.chopperPhase:
+        para += f' --chopperPhase {clas.chopperPhase}'
+    if clas.chopperPhaseOffset:
+        para += f' --chopperPhaseOffset {clas.chopperPhaseOffset}'
+    if clas.mu:
+        para += f' --mu {clas.mu}'
+    elif clas.muOffset:
+        para += f' --muOffset {clas.muOffset}'
+    if clas.nu:
+        para += f' --nu {clas.nu}'
+
+    if clas.sampleModel:
+        modl =  f" --sampleModel '{clas.sampleModel}'"
+
+    acts = ''
+    if clas.autoscale:
+        acts += f' --autoscale {clas.autoscale}'
+    if clas.scale:
+        acts += f' --scale {clas.scale}'
+    if clas.timeSlize:
+        acts += f' --timeSlize {clas.timeSlize}'
+
+    mlst = base + '\n' + inpt + '\n' + outp 
+    if mask:
+        mlst += '\n' + mask
+    if para:
+        mlst += '\n' + para
+    if acts:
+        mlst += '\n' + acts
+    if mask:
+        modl += '\n' + modl
+
+    return  mlst