Calculations in Virtual Feeds failing

Perhaps I’m doing something wrong, some help would certainly be appreciated.

Since I fitted a new preinstalled sdcard I’m having an issue with Feeds that are ‘Virtual’ and have calculations. The value of these feeds is always ‘ZERO’ now. They always worked before.

Here is an example.

Here are the two source feeds I’m using.

Here is the Virtual Feed.

And its result is shown as ‘ZERO’

Am I misunderstanding the use of Virtual Feeds?

Hello @Mike_Henderson this should work fine, testing here it seems to work for me with the multiplication in the same way that you have it configured.

Could you copy and paste here the system info from the emoncms admin/info page?

Server Information

	emonhub :	 Active Running                      
	emoncms_mqtt :	 Active Running                      
	feedwriter :	 Active Running - sleep 300s 1557 feed points pending write
	service-runner :	 Active Running                      
	emonPiLCD :	 Active Running                      
	redis-server :	 Active Running                      
	mosquitto :	 Active Running                      
	demandshaper :	 Not found or not installed                                  
	Version :	 low-write 11.2.10
	Git :	 
		URL :
		Branch :	 * stable
		Describe :	 11.2.10
	Components :	 Emoncms Core v11.2.10 | App v2.6.8 | EmonHub Config v2.1.5 | Dashboard v2.3.3 | Device v2.2.2 | Graph v2.2.3 | Network Setup v1.0.2 | WiFi v2.1.1 | Backup v2.3.2 | Postprocess v2.2.7 | Sync v2.1.4 | Usefulscripts v2.3.10 | Avrdude-rpi v1.0.1 | Emonhub v2.5.2 | EmonPi v2.9.5 | EmonScripts v1.5.14 | RFM2Pi v1.4.1

	CPU :	 1 Threads(s) | 4 Core(s) | 1 Sockets(s) | Cortex-A53 | 89.60MIPS | 
	OS :	 Linux 5.15.76-v7+
	Host :	 emonpi | emonpi | (
	Date :	 2023-01-08 11:25:01 UTC
	Uptime :	 11:25:01 up 2 days, 16:44,  0 users,  load average: 0.28, 0.30, 0.29

	RAM :	 Used: 19.30%
		Total :	 922.14 MB
		Used :	 178 MB
		Free :	 744.14 MB
	Swap :	 Used: 76.96%
		Total :	 100 MB
		Used :	 76.96 MB
		Free :	 23.04 MB

	 :	 - / :	 Used: 40.41%
		Total :	 5.78 GB
		Used :	 2.33 GB
		Free :	 3.13 GB
		Read Load :	 1.1 KB/s
		Write Load :	 2.05 KB/s
		Load Time :	 2 days 16 hours 31 mins
	/boot :	 Used: 19.52%
		Total :	 254.99 MB
		Used :	 49.78 MB
		Free :	 205.21 MB
		Read Load :	 0.02 B/s
		Write Load :	 0 B/s
		Load Time :	 2 days 16 hours 31 mins
	/var/opt/emoncms :	 Used: 17.58%
		Total :	 9.61 GB
		Used :	 1.69 GB
		Free :	 7.43 GB
		Read Load :	 28.05 KB/s
		Write Load :	 8.54 KB/s
		Load Time :	 2 days 16 hours 31 mins
	/var/log :	 Used: 16.24%
		Total :	 50 MB
		Used :	 8.12 MB
		Free :	 41.88 MB
		Read Load :	 n/a
		Write Load :	 n/a
		Load Time :	 n/a

	Server :	 Apache/2.4.54 (Raspbian) HTTP/1.1 CGI/1.1 80

	Version :	 10.5.15-MariaDB-0+deb11u1
	Host : (
	Date :	 2023-01-08 11:25:00 (UTC 00:00‌​)
	Stats :	 Uptime: 233138  Threads: 11  Questions: 940376  Slow queries: 0  Opens: 60  Open tables: 53  Queries per second avg: 4.033

	Version :	 
		Redis Server :	 6.0.16
		PHP Redis :	 6.0.0-dev
	Host :	 localhost:6379
	Size :	 948 keys (928.36K)
	Uptime :	 2 days

MQTT Server
	Version :	 Mosquitto 2.0.11
	Host :	 localhost:1883 (

	Version :	 8.1.12 (Zend Version 4.1.12)
	Run user :	 User: www-data Group: www-data video Script Owner: pi
	Modules :	 apache2handler calendar Core ctype curl date dom v20031129exif FFI fileinfo filter ftp gd gettext hash iconv json libxml mbstring mosquitto v0.4.0mysqli mysqlnd vmysqlnd 8.1.12openssl pcre PDO pdo_mysql Phar posix readline redis v6.0.0-devReflection session shmop SimpleXML sockets sodium SPL standard sysvmsg sysvsem sysvshm tokenizer xml xmlreader xmlwriter xsl Zend OPcache zlib 
	Model :	 Raspberry Pi 3 Model B+ Rev 1.3 - 1GB (Sony UK)
	Serial num. :	 76AB6BF1
	CPU Temperature :	 48.31°C
	GPU Temperature :	 N/A (to show GPU temp execute this command from the console "sudo usermod -G video www-data" )
	emonpiRelease :	 emonSD-10Nov22
	File-system :	 read-write

Client Information

	Browser :	 Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/ Safari/537.36
	Language :	 en-GB,en-US;q=0.9,en;q=0.8

	Size :	 1657 x 793

	Resolution :	 1920 x 1080

Thanks, all looks fine, when you look at the graph for that vitual feed is it also zero? What about a virtual feed with source feed only? What are the feed intervals? and what happens if you enable averaging on the graph page? I wonder if it’s null values in the feeds tripping it up…

Ok, I’ve made up this test feed.

The source feed has a feed interval of 10 seconds.

I have just noticed when I graph the source feed that the last value is always ‘null’

This’ll be why when I try to place a value from the virtual feed on a dashboard it will show zero as it’s trying to use the last saved value, but my graphs of the virtual feed continue to show data.

I notice that when I check the CSV data of the trend, the last ‘NULL’ value is from a timestamp ahead of the clock.


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Looks like I was testing above with an older version. Testing on the latest I was able to replicate and have now fixed the issue and pushed up the update. Version is now 11.2.11 available in both master and stable.


Cheers :slight_smile:
I see numbers other than ‘0’.

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@TrystanLea, could you close issues on GitHub with a link to the fix commit/release when you fix things, please :slight_smile:

If I had more hours in the day yes! I’ve closed @greentangerine issue, thanks Nick!
Release notes need looking at as there’s quite a bit of change since the last stable release vs stable tag.


Seems to be Ok for me too.


This appears to still be an issue. I’m using Version
low-write 11.3.0 and the virtual feed value is NULL.

Still working here with V11.3.0

However I did notice another I use elsewhare had stopped working a couple of days ago - I will try to check that again next week.

I can draw a graph and see the values, however I only see “0” in other widgets, such as a “dial” in a dashboard.

I am experiencing the same issue; “0” is displayed in single value widgets, such as a “dial”.

I guess that the code should display the value [n-1], since value [n] is null ?

Virtual feeds are working fine on my local dashboard, but I have the same issue as you describe using emoncms online dashboard.

Virtual feeds show as ‘0’, but any graphs with virtual feeds in them display fine - although it is evident that the latest value on the graph for the virtual feed is zero.

Hope that makes sense.

My local dashboard works correctly also. It would appear as though there is an issue with the dashboard.

Is there a resolution to this issue? Thank you.