# Differences

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manual:087:7_examples [2010/02/21 17:45]
gandalf continued
manual:087:7_examples [2019/10/29 15:16] (current)
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===== Graphing Data with a Small Standard Deviation ===== ===== Graphing Data with a Small Standard Deviation =====
+
+Sometimes, the automatic scaling of y-axis fails.
+
+**Example:**
+<code>/usr/bin/rrdtool graph - \
+--imgformat=PNG \
+--end=now \
+--start=end-150000 \
+--title="Small Standarddeviation" \
+--slope-mode \
+DEF:a="test.rrd":test:AVERAGE \
+CDEF:sine=a,POP,NOW,TIME,-,10000,/,SIN,1000,+ \
+LINE1:sine#0000ff:sine</code>
+
+{{:manual:087:small-stddev.png|Small Standarddeviation using defaults}}
+
+==== Using --alt-autoscale ====
+
+In this case, using --alt-autoscale helps:
+**Example:**
+<code>/usr/bin/rrdtool graph - \
+--imgformat=PNG \
+--end=now \
+--start=end-150000 \
+--title="Small Standarddeviation using Autoscale" \
+--alt-autoscale \
+--slope-mode \
+DEF:a="test.rrd":test:AVERAGE \
+CDEF:sine=a,POP,NOW,TIME,-,10000,/,SIN,1000,+ \
+LINE1:sine#0000ff:sine</code>
+
+{{:manual:087:small-stddev-autoscale.png|Small Standarddeviation using --alt-autoscale}}
+
+That indeed looks better. But you can't judge from this graph, how big the amplitude of the sine is.
+
+==== Using --alt-autoscale and --alt-y-grid ====
+
+Using the alternate grid (--alt-y-grid) solves this problem.
+
+**Example:**
+<code>/usr/bin/rrdtool graph - \
+--imgformat=PNG \
+--end=now \
+--start=end-150000 \
+--title="Small Stddev using Autoscale and --alt-y-grid" \
+--alt-autoscale \
+--alt-y-grid \
+--slope-mode \
+DEF:a="test.rrd":test:AVERAGE \
+CDEF:sine=a,POP,NOW,TIME,-,10000,/,SIN,1000,+ \
+LINE1:sine#0000ff:sine</code>
+
+{{:manual:087:small-stddev-autoscale-alt-y-grid.png|Using --alt-y-grid to adjust y-axis}}