# Differences

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manual:087:7_examples [2010/02/21 17:31]
gandalf created
manual:087:7_examples [2019/10/29 15:16] (current)
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This way, the graphs y-axis will automatically adjust for the range of values displayed. The common drawback is, that you will have to pay attention for the current y-axis scale, because it "jumps" from low to high values. This way, the graphs y-axis will automatically adjust for the range of values displayed. The common drawback is, that you will have to pay attention for the current y-axis scale, because it "jumps" from low to high values.

-==== Using an Upper Limit ====+===== Using an Upper Limit =====

In order to define the same y-axis dimensions for a graph template, In order to define the same y-axis dimensions for a graph template,
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{{:manual:087:upper-limit.png|Upper Limit, when limit is not exceeded by data}} {{:manual:087:upper-limit.png|Upper Limit, when limit is not exceeded by data}}

-=== Data exceeds given Limit ===+==== Data exceeds given Limit ====

-The following example uses the same graph configuration. But the data was tweaked to excee the given limit. You will notice, that rrdtool automatically extends the y-axis despite the given --uper-limit!+The following example uses the same graph configuration. But the data was tweaked to exceed the given limit. You will notice, that rrdtool automatically extends the y-axis despite the given --upper-limit!

**Example:** **Example:**
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{{:manual:087:upper-limit-exceed.png|Upper Limit, when limit **IS** exceeded by data}} {{:manual:087:upper-limit-exceed.png|Upper Limit, when limit **IS** exceeded by data}}

+==== Data exceeds given Limit, Capped ====

-==== Graphing Negative Values ====+The following example uses the same graph configuration; data tweaked to exceed the given limit. Now we use
+  * check **Auto Scale**
+  * select **--alt-autoscale-min (accepting an upper limit, requires rrdtool 1.2.x)**
+  * define a numeric value for **upper limit**. e.g. 2
+  * check **Rigid Boundaries Mode (--rigid)**

+**Example:**
+<code>/usr/bin/rrdtool graph - \
+--imgformat=PNG \
+--end=now \
+--start=end-150000 \
+--title="Upper Limit" \
+--alt-autoscale-min \
+--upper-limit=2 \
+--rigid \
+--slope-mode \
+DEF:a="test.rrd":test:AVERAGE \
+CDEF:sine=a,POP,NOW,TIME,-,10000,/,SIN,3,* \
+LINE1:sine#0000ff:sine</code>
+
+{{:manual:087:upper-limit-exceed-capped.png|Upper Limit, capped, when limit **IS** exceeded by data}}
+
+**Notice**:\\ Please note, that the upper y-axis is capped only, as we use **--upper-limit**
+
+
+===== 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>

-==== Graphing Data with a Small Standard Deviation ====+{{:manual:087:small-stddev-autoscale-alt-y-grid.png|Using --alt-y-grid to adjust y-axis}}