We have a web application that lists prices of a stocks and we have a requirement to indicate a movement. When there's an increase in price we add an up arrow, where there's a decrease in price we add a down arrow.
My thoughts are that we don't show anything as it's not moving, but I would like to validate this. The options that I see are:
What is the standard for indicating a values movement?
A fairly standard method is to use a horizontal arrow pointing towards the unchanged figure. If you use colour — red and green for up and down (whichever) — "unchanged" could be grey.
Addendum: It is important to show something! A gap could be interpreted as "We can't tell whether this has moved," "We know this is out of date," or an image which hasn't loaded yet. Since you are indicating movement in the figures, you do need to indicate that you have assessed movement in all the figures where you have actually done that.
While I agree that a symbol could be used to indicate each of the 3 states, I would also recommend using colour - perhaps red for price drop, green for price rise, black for no change. I wouldn't only use colour, primarily because of red-green colour blindness, but for a majority of people it would be a quicker visual cue to get an overview than using symbols.
Because you are using arrows to indicate up and down, keep the iconography consistent, and use an arrow for no change - pointing sideways, either to the figure, or a double headed arrow pointing both ways.
Mixing the images would be confusing, so keep it consistent. Colour it black or grey - something to indicate neutrality, and the up ones green an the down ones red (or vv if that makes more sense). This means that for most people, they can look at the screen and identify the predominant colour showing easily, and get a very quick overview. Keeping the "no change" neutral means it doesn't interfere with this.
I would uderstand this betrer >=< as it to me represents no movement in either direction. I'd interpret <=> as flexible movement in either direction.... just an opinion.