minor documentation fixes

[jonathancallahan]

Please leave this issue open

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TODO:

• PurpleAirSoH_dailyABtTest() -- " hover near 0" should be substituted with an alpha value since we are analyzing p-values. How can we reject or fail to reject the Null hypothesis without alpha?
• PurpleAirSoH_dailyMetFit() needs to specify that daily r-squared values are
  expected to hover near 0 (how close?) for a properly functioning sensor under normal
  environemntal conditions. During the wildfire season or winter time when home heating systems are heavily used, we actually expect fluctuating R squared values.
• PurpleAirQC_hourly_AB_03() needs correction -- "AB_O4" should be "AB_O3".
• pat_externalFit() -- it would be helpful to have a few sentences describing the graphs, and what are the minumum expected values for slope and R sq. Here we are comparing PA sensor data to Monitor data, how tolerant can we be in assessing their relationship?
• sensor_polarPlot() should include something like "If not specified, wind data of the nearest airport station are used. The data is obtained with the worldmet package".
• sensor_polarPlot() -- add a brief plot interpreation and add wind speed unit
• sensor_polarPlot() -- what is "polarFreq" in statistic descriptions?
• sensor_polarPlot() -- more details needed about how to interpret the statistic scale.
• sensor_pollutionRose() -- add a brief plot interpreation and add wind speed unit
• timeseriesTbl_multiPlot() -- doc missing, error 404
• pat_multiPlot() -- doc missing, error 404

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Items finished on 2021-03-10

• pat_load() needs to mention default time range when none is specified
• in the pat_dygraph example online the use of ‘rollperiod’ is confusing. Why 6?

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