There’s some great info here!
@GaryFunk uses a 60 minute (or 90) window with a change of +/-5 C defining a trend, and a +/- 10 C change defining a rapid trend.
@Weather34 uses a shorter window (15 minutes) that is going to be more responsive to shorter timescale variability. You don’t mention what cutoffs you use to define a trend, however. Does a minimum change have to occur over 15 minutes, or do you take any change as the trend?
i dont use a cut off to detect or highlight the movement of rising or falling. if no change in 15 minutes then obviously steady . using the shorter interval it will,always reflect the change as it is a rolling fifteen minutes .
i.e if time now is 15:50 it will look for temp at 15:35 or if time now 15:51 it will look for temp at 15:36 and output the difference in plus or minus in my case an arrow .
i also have a seperate alert box for rapid changes i.e if temp dropped 10c in 15 minutes or 30 minutes it produces an alert. my approach is just simply detecting the minor changes and i found this to be a good indictator of change or imminent changes if they are going to occur.
for here in this location a change a of 2c in dewpoint is really really noticeable especially in summer months , my body feels comfortable at 19c dewpoint and below when it starts creeping above 20c i begin to sweat quite noticeably so i use the small changes for monitoring dewpoint as indicator of what sort of. night im going to have . its a personal preference.
the change is always reflected no matter how small or large in the template.as shown below .
so in short shorter intervals work for me rather than the longer hourly change. 
Brian your template looks good but the icon for trend is a little bit off - shows falling, then rising, than falling? Or rising, falling and then rising. Considering your way calculating trend that is not possible. Its falling, or rising.
sorry i don’t understand
If you take your trend-icon as a graph it shows a “history”. First something (fx temp) is rising, then falling and then rising if you follow the trend line. I will argue that the line should go up (rising trend), or down (falling trend).
I would use something like this: http://cdn.onlinewebfonts.com/svg/img_452708.png (the arrow)
Software Cumulus bases the trend on 3 hours (The average rate of change in temperature over the last three hours. Trend = (temp_now - temp_3hrs_ago) / 3)
I could not find where this timespan comes from but probably this is the way how Davis Instruments handles the ‘trend’
Anyway ‘trend’ is used in many timespans we have to call the WMO 
temperature is faling
humidity is rising
dewpoint is rising
quite simple
No, that is not what your trend-icon shows.
hmmm think your confusing something else i see arrow rising dewpoint,humidity and falling arrow for temperature last 15 minutes.
Your icons shows more than a trend, your icons shows a graph (that shows a history). That is wrong. But ok, we will never agree.
I think droiddk means you need an arrow without ups and downs
im sorry no idea of what what your getting at , i see two arrows one rising one falling … nothing to agree on if i dont quite understand back to the subject trend on the app…
Exactly, spot on.
…
sorry i truly do not follow . so i see i dont know what yor saying give me something visual i may see what your saying
I would use something like this: http://cdn.onlinewebfonts.com/svg/img_452708.png (the arrow) Without ups and downs.
Well the trendarrow by example for tempgoes doown then a bit up and then down I know the intention but strict it says the temp was falliing rising and falling in pint of history (but in my eye of view you can leave it as it is)
i get that part but do the arrows not indicate rising or falling .
ok i agree ron but the arrow does point down or up so i think ill just leave it its been like that for a few years . i don’t disagree ron your quite right but i dont see it will make a lot of difference.
What arrow is used when there is no change , so steady ?
