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This page is the new ''Recent History'' page. This page is part of a complete rewrite of the ''Webtags'' page.
As long as this message exists please refer to [[Recent History (preserving history)]].
This page is Work in Progress until this message is deleted.
If any questions or remarks please send a PM to [https://cumulus.hosiene.co.uk/memberlist.php?mode=viewprofile&u=9016 HansR] on the forum. Do not use the ''discussion'' tab unless accompanied by a PM: there is  no automated signal to HansR if you use that page.
This page and its subpages will document the Webtags from the point of view of the CumulusMX software and not the Cumulus 1 legacy software. Cumulus 1 is no longer maintained and will eventually disappear. If you are still using it, please refer to the original [[Webtags_(preserving_history)|Webtags]] page where @sfws has tried to give both packages equal value. That effort is no longer maintained in this page. We hope you will understand this approach.
Please do not edit this page while it is being worked on i.e. while this message is still here.
<hr/>
[[Category:Terminology]] [[Category:Cumulus Files]]
[[Category:Terminology]] [[Category:Cumulus Files]]


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There are a number of internal calculations, such as calculating [[Average temperature]], [[Heat/cold degree days and Chill hours]], which use the recent history data stored in the Recent History Database for CumulusMX. These data are also used for the standard [[MX_Administrative_Interface#Charts|charts]] and the JSON data for the charts on the standard website and many other websites. See: [[:Category:JSON_Files#Uploading_data_to_a_web_server_outside_MX:|Uploading data to a webserver outside CumulusMX ]] .
There are a number of internal calculations, such as calculating [[Average temperature]], [[Heat/cold degree days and Chill hours]], which use the recent history data stored in the Recent History Database for CumulusMX. These data are also used for the standard [[MX_Administrative_Interface#Charts|charts]] and the JSON data for the charts on the standard website and many other websites. See: [[:Category:JSON_Files#Uploading_data_to_a_web_server_outside_MX:|Uploading data to a webserver outside CumulusMX ]] .


=Which weather values are stored?=
== Which weather values are stored ==


For '''Current Conditions''', Cumulus can display values from the basic set of weather sensors it expects, from some derived values, and from various extra sensors, as per table below.
For '''Current Conditions''', Cumulus can display values from the basic set of weather sensors it expects, from some derived values, and from various extra sensors, as per table below.
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As Cumulus has been developed, more and more of these have been stored for Recent History. Those available in current version of CumulusMX release are listed at [[cumulusmx.db|RecentData table in cumulusmx.db]].
As Cumulus has been developed, more and more of these have been stored for Recent History. Those available in current version of CumulusMX release are listed at [[cumulusmx.db|RecentData table in cumulusmx.db]].


=Warning when Daylight Saving Time starts or ends=
== Warning when Daylight Saving Time starts or ends ==


'''Please note that parameters specify time-stamped array element to retrieve based on counting back from current local time''' so the result for ''any period including when clocks change'' may not be quite what you anticipated.
Please note that parameters specify time-stamped array element to retrieve based on counting back from current local time so the result for ''any period including when clocks change'' may not be quite what you anticipated.


== Changing from Summer to Winter time==
=== Changing from Summer to Winter time ===


Remember, ''when clocks go back'', that for a whole hour following the clock change, clock times (now in winter time) repeat the previous clock times (that were in summer time).  The way that Cumulus has coded this functionality, instead of the new sets of spot values being added after the old rows/elements, they overwrite the old table rows, or array elements, for the same times.  Consequently, you cannot retrieve any values for the times that have been overwritten, and you must be careful when you specify to Cumulus which values you wish to retrieve.
Remember, ''when clocks go back'', that for a whole hour following the clock change, clock times (now in winter time) repeat the previous clock times (that were in summer time).  The way that Cumulus has coded this functionality, instead of the new sets of spot values being added after the old rows/elements, they overwrite the old table rows, or array elements, for the same times.  Consequently, you cannot retrieve any values for the times that have been overwritten, and you must be careful when you specify to Cumulus which values you wish to retrieve.


==Changing from Winter to Summer time==
=== Changing from Winter to Summer time ===


As for ''when the clocks go forward'', the new values do get added after the old rows/elements, but of course there will be one hour's worth of times that simply do not exist.  Consequently, any attempt to retrieve values around the time of the clock change has to be careful not to specify any time in that non-existent period, as Cumulus will just return the value before, or the value after, depending on which is nearest.
As for ''when the clocks go forward'', the new values do get added after the old rows/elements, but of course there will be one hour's worth of times that simply do not exist.  Consequently, any attempt to retrieve values around the time of the clock change has to be careful not to specify any time in that non-existent period, as Cumulus will just return the value before, or the value after, depending on which is nearest.


==Technical note==
=== Technical note ===


As explained earlier, you request an entry from Recent History by specifying 1 to 10 079 minutes ago. Cumulus looks at current clock time, calculates what time would be that long ago, and seeks the nearest datetime entry.
As explained earlier, you request an entry from Recent History by specifying 1 to 10 079 minutes ago. Cumulus looks at current clock time, calculates what time would be that long ago, and seeks the nearest datetime entry.
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However, to do this would involve more complicated code, because MX would need to keep track of which row was last updated, keep track of when the clocks changed, and modify its search routine to find the correct row. Life is much easier if the Cumulus user makes allowance for any clock change when making their request.
However, to do this would involve more complicated code, because MX would need to keep track of which row was last updated, keep track of when the clocks changed, and modify its search routine to find the correct row. Life is much easier if the Cumulus user makes allowance for any clock change when making their request.
=If the derivative you want is not available in your Cumulus release=
It was mentioned [[#Which weather values are stored?|earlier]] that more recent history web tag names have been added as Cumulus developed.  In many cases, Cumulus has actually started calculating the derivative and using it for charts, in earlier releases than when it becomes available for others to use via web tags.
From 3.12.0, the availability of the database for viewing outside Cumulus, means that anyone who knows how to read a SQLite database can write a script, or program, to access any derivative that is in the database, but not available as a web tag, and can then pass the output to their web site by an appropriate technical process.
Alternatively, although Humidex, 'Apparent Temperature', 'Feels Like temperature', and other derivatives Cumulus can calculate, are not available in all releases, they can be calculated in a script from recent 'outside temperature', 'wind speed', and 'relative humidity' values (using the same time selection for all).
There are other derivatives that can be calculated similarly from a set of simultaneous values. Note that Cumulus 1 and MX do not always use identical formula, and although MX added Feels Like it has changed the formula a few times.
The relevant formulae using JavaScript, you need to adjust them for other languages, for some of these are shown below:
== Canadian Humidity Index ==
If you are in USA and use Fahrenheit instead of Celsius, you will need to omit the 5/9 term, but as the index is dimensionless no other conversion is needed. This example is for 3 hours ago, change the input modification parameter to suit your need.
Cumulus 1:
H = <#RecentOutsideTemp h=3> + 5/9 * (6.1094 * Math.exp(5417.753 *(1/273.16 - 1/ (273.16 + <#RecentDewPoint h=3> )))-10);
Cumulus MX:
svp = 6.112 * Math.exp((17.62 * <#RecentOutsideTemp h=3) / (243.12 + parseFloat(<#RecentOutsideTemp h=3)));
H = (5/9 * (<#RecentHumidity h=3> /100 * svp - 10)) + <#RecentOutsideTemp h=3;
== Apparent Temperature and Feels Like ==
Note this apparent temperature formula uses Celsius for temperature and '''metres per second''' for wind speed. You will need to do the appropriate conversions from the quoted recent history tags if you use different units.  The Australian Apparent temperature formula is same for Cumulus 1 and MX:
var actualVaporPress = <#RecentHumidity h=3>/100) * 6.105 * Math.exp(17.27 * <#RecentOutsideTemp h=3>) / (237.7 + parseFloat(<#RecentOutsideTemp h=3>))));
var appTempDegC = parseFloat(<#RecentOutsideTemp h=3) + (0.33 * actualVaporPress) - (0.7 * <#RecentWindSpeed h=3>) - 4;
Feels Like was implemented as a recent history web tag at version 3.6.11 (see [[#Feels_Like|Feels Like section below Current condition web tags]]) for the gradual introduction of feels like elsewhere. For earlier MX versions, and if you are using Cumulus 1, you can calculate it:
The formulas below use Celsius for temperature and '''km per hour''' for wind speed. Again, you will need to do the appropriate conversions from the quoted recent history tags if you use different units.
Calculation from recent history tags is much more complicated because there are 3 different calculations: Feels Like reports exactly same as wind chill for temperatures '''below''' 10°C or 50°F so the WC here should equal <#RecentWindChill h=3>:
<pre>if(<#RecentWindSpeed h=3> < 4.828) WC =  <#RecentOutsideTemp h=3>;
else{
wind_pow =  Math.pow(<#RecentWindSpeed h=3>, 0.16);
WC = (13.12 + 0.1625 * <#RecentOutsideTemp h=3>) - (11.37 * wind_pow) + (0.3965 * <#RecentOutsideTemp h=3> * wind_pow);// Brackets used to ensure "+" is interpreted as addition not concatenation
} </pre>
For temperatures '''above''' 20°C or 68°F Feels Like uses a different way to calculate apparent temperature that it uses at these higher temperatures (this formula only used for 3.6.10 onwards):
<pre>var actualVaporPress = <#RecentHumidity h=3>/100) * 6.112* Math.exp((17.62 * <#RecentOutsideTemp h=3>)/(243.12 + <#RecentOutsideTemp h=3>)) / 10.0;  // Not same as at build 3084
/* uses kilometres per hour for wind speed */
/*  What Cumulus MX will use to calculate apparent temperature for feels like is changed very slightly */
if(<#RecentWindSpeed h=3> > 72) <#RecentWindSpeed h=3> =72;
AT= (1.04 * <#RecentOutsideTemp h=3>) + (2 * actualVaporPress) - (0.1805553 * <#RecentWindSpeed h=3>) - 2.7;</pre>
For in-between temperatures it uses a more complicated merge of the two formulas for AT and WC as defined above:
<pre>app_temp_mult = (<#RecentOutsideTemp h=3> - 10) / 10;
wind_chill_mult = 1 - app_temp_mult;
FL= AT * app_temp_mult + WC * wind_chill_mult;</pre>
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