diff --git a/slurm-eff-tool.py b/slurm-eff-tool.py
index daaf163..e48a16a 100755
--- a/slurm-eff-tool.py
+++ b/slurm-eff-tool.py
@@ -239,7 +239,7 @@ HISTO_COLUMNS = {
     "Mem_Eff",
     "Planned_Time",
     "Time_Eff",
-    "UsesMem",
+    "UsedMem",
     "Walltime",
  }
 
@@ -1025,7 +1025,7 @@ def make_single_row(rec: JobRecord, dflt_mpcpu: float,
             vectors[colname] = []
             if colname == "walltime":
                 vectors[colname] = [rec.elapsed_sec/3600]
-            elif colname == "used_mem" and rec.mem_used_tres is not None:
+            elif colname == "usedmem" and rec.mem_used_tres is not None:
                 vectors[colname] = [rec.mem_used_tres]
             elif colname == "elig_qtime":
                 vectors[colname] = [rec.elig_qtime_sec/3600]
@@ -1134,7 +1134,7 @@ def make_aggregate_row(records: list[JobRecord], username: str, partition: str,
             if colname == "walltime":
                 vectors[colname] = [r.elapsed_sec/3600 for r in records
                                     if r.elapsed_sec is not None]
-            elif colname == "used_mem":
+            elif colname == "usedmem":
                 vectors[colname] = [r.mem_used_tres for r in records
                                     if r.mem_used_tres is not None]
             elif colname == "elig_qtime":
@@ -1283,10 +1283,9 @@ def columns_from_fmtstr(fmt: str) -> list[str]:
 from bisect import bisect_right
 from collections.abc import Iterable, Sequence
 from math import ceil, exp, floor, log, log10
-from typing import TypeAlias
 
 
-Metricnumber: TypeAlias = int | float
+Metricnumber = Union[int, float]
 
 
 def percentile(sorted_values: Sequence[float], p: float) -> float:
@@ -1490,10 +1489,14 @@ plot_cmd = 'plot "{tmpfile.name}" \\
 
         gnuplot_cmd += "'\neval plot_cmd\n"
         # print(f"DEBUG: GNUPLOT_SCRIPT:\n{gnuplot_cmd}")
-        run(["gnuplot"],
-            input=gnuplot_cmd,
-            text=True,
-            check=True,)
+        try:
+            run(["gnuplot"],
+                input=gnuplot_cmd,
+                text=True,
+                check=True,)
+        except FileNotFoundError:
+            sys.stderr.write("ERROR: Cannot execute gnuplot for histogram creation. Is it installed?\n")
+            sys.exit(1)
         os.remove(tmpfile.name)
     
 # HISTOGRAMMING CODE END