Comments on VisAGE Displays from Professional Participants in the Usability Study (May, 1998)

The study used two data feeds from heater sources. One source comprised heaters 1 and 2; the other comprised heaters 1, 2, 3, 4, and 5. Participants were asked to respond to questions about heater (Htr) temperatures and trends. They were also asked to provide comments reflecting their assessment of the various displays. The comments are presented here as written by the professional participants; text enclosed in brackets ([]) is occasionally added to aid readability.

2D Text:

1. Compared to the pie chart, it is much harder to tell what is happening but easier to see exact readings.

1. Two lines of data are easier to watch than five. It is still harder [than with the pie chart] to see what the temperatures are doing.

1. Heater list in numeric order [from top down] would be better. [I was] surprised to see Heater 5 on top. I would find this ordering distracting to work with unless there was some physical reason for it.

1. No history [of prior values]

1. Order problem: [the reverse of expected.] Heaters should be numbered 1-5 from the top down.

1. This is analogous to the alphanumeric page displays in control centers. The thing that is confusing here is the rate at which values are being updated. Most of the time, analysis is not performed by looking at pages in realtime and visually analyzing where numbers are trending. POCC graphing functions are used for this.

1. [I] expect 1-5 going down the page, not up.

1. [It’s] hard to remember the trend [with this display].

1. Do temperatures [or any values] have to be taken out to 5 decimal places?

2D Histogram/Bar chart:

1. The scale kept changing. The boxes appeared to be rising and falling, but the scale on the left kept changing so the bar may appear to grow, but the temperature may have been falling.

1. The bars seem to be in the reverse order of how I would expect them. I would expect to see Htr 1 on the left and Htr 2 on the right.

1. [I] don’t like to have the scale changing. [I] thought the constantly changing y-axis values were confusing. [I] would like to have seen it fixed.

1. This type of display is good for making comparisons if the scale is stable.

1. Numeric order [left to right] for labels [would be better].

1. [There was a] color problem. [Two bars were black , and a third bar was nearly black, making it hard to tell which heater was which. ] [Note: This seemed to be an artifact and occurred only for one participant. Generally, colors were distinguishable, although the choice of colors should be guided by human factors guidelines.]

1. My expectation of which field represented heaters 1 and 2 were not met. HTR2 was on the left, when I expect HTR1 on the left.

1. [There is] no time that I can interpret. The y-scale is too coarse to draw any meaningful conclusions about values.

1. This chart may be useful for thruster-pulse counting and related fuel usage.

1. This chart could be used to monitor values that must be reached before a function on the spacecraft can be executed.

1. [It] would be nice to have labels with HTR1 on top and bars going left to right starting with HTR1.

2D Strip Chart:

1. Easy to see history and trends. I immediately see how close they are when they switch over, which I didn’t catch before [from the previous 3-D text display].

1. I don’t like the scale changing.

1. [With five heater sources, this display is] busy.

1. Typically only need time, not date, on the independent [x] axis.

1. Dependent [y] axis scale is too coarse to accurately analyze data.

1. [With this display,] at least I can answer your questions with a reasonable degree of confidence.

1. Add text of current values for the heaters.

1. Add a vertical and horizontal grid option to this graph.

1. Having HTR 1 on the bottom is confusing. Usually number from top to bottom.

1. Times are difficult to read (always need date?).

1. [I’m] not sure if the data samples are at the line marks or the times at the bottom of the graph.

2D Pie Chart:

1. [The area of a] pie chart is assumed to be a total, so if one is going up [increasing in area], the other is going down [decreasing in area]; but this may not actually be the case. So while I initially thought Htr 2 was going up and Htr 1 was going down, actually you can’t tell from this display.

1. No labels — hot or cold is greater?

1. No history [of previous values]

1. Very difficult to compare values.

1. Order problem [in the legend for the heaters: order is the reverse of expected.]

1. Two [heaters] correlated (perfectly) are redundant.

1. This type of representation offers me no visibility into the performance of these mnemonics. [There is] no time representation or understanding of how these perform over time.

1. If this graph shows number of degrees for heater 1 vs. number of degrees for heater 2, then the size of the pie is actually varying, and perhaps that aspect should be shown too.

1. [I had to make the ] assumption that greater % of area equaled higher temperature value. Add text values [for slices of the pie].

1. For a spinning [i.e., rotating] spacecraft, this chart could be used to display changes in solar panel output, using one pie chart per solar panel.

1. I assumed that larger area means greater value [although this may not necessarily be the case].

1. [I’m] not sure what the purpose of this display was.

1. [I] would like to have labels on the pie chart [as on the other displays]. Colors alone are hard to match up.

3D Text:

1. Text data seems best displayed in 2D. Text is text.

1. This is silly.

1. Order problem [in labeling: The reverse of expected.]

1. This is the stupidest thing I’ve ever seen, though it’s impressive that you can do it.

1. [It’s] dumb [to have controls] for a bunch of numbers.

1. Choose a new color for the text. I find red irritates the eyes. [Note from researcher: Red on black is specifically not recommended in color display guidelines. Unless there is some reason why the background has to be black, it would be better to pick a more neutral background (grey, beige) and a foreground color that will be in good contrast to the background. ]

1. Text only needs to be viewed in 2D. Rotating [and the other movements] only make it harder to read. [I] can easily read text in 2D.

3D Histogram/Bar Chart:

1. [The third dimension does not aid my understanding of the data] because bars only change in two dimensions.

1. Numbers are hard to read. Had to zoom out to see labels and then zoom in to read numbers.

1. Numeric order problem [with labels]. [Numbers should read in order from left to right, not right to left (e.g., 1, 2, 3, 4, 5 not 5, 4, 3, 2, 1).] List labels from left to right (1, 2, 3, 4, 5). [Note: the backwards listing violates standard practice and tends to induce errors of misreading because the person expects Heater 1 to be in the position occupied by Heater 5.]

1. [This display provides] no history information.

1. Actually, the bar chart is not a very useful representation for spacecraft telemetry. In most analysis functions, one is interested in variability over time, where time is in minutes for short-term analysis or months and years for long-term trends. Also, no graphics [I have seen] to date [in the study] have been very intuitive. I expected to read increasing heater number 1, 2…5 from left to right in this case.

1. You can see the bar growing or diminishing if you’re watching it, but you have to remember where the bar has been. Numbers are hard to read.

1. The text on the graph should be the same color as that used for the data points.

1. This chart may be used to study anomalies that may result in secondary anomalies. This chart would show the delay between [the first and second anomalies]. That delay might provide information on the actual anomaly.

1. The values are hard to read on top of grid lines. Values are displayed in yellow text. The grid is white. [Note from researcher: White on yellow is a combination specifically not recommended in color guidelines. It does not give enough contrast.]

1. Data can be easily seen in 2D. A third dimension doesn’t provide additional information [for these 2D data]. Bar charts are easily viewed in 2D.

3D Strip Chart:

1. [It was] hard to find a good view to see the labels and data and how they match up.

1. [You] have to manipulate a lot to understand the data.

1. Order problem: [heaters are labeled back to front (e.g., 1 to 5 from the back) instead of front to back (e.g., 1 to 5 from the front). This is the reverse of standard practice.]

1. I cannot distinguish between five data streams that have no visually distinguishing characteristics.

1. I could not use this for analysis. [It] lacks numerically labeled axes, in engineering units and time. The three dimensional image on the flat screen mashes all the labels together. [I] had to rotate the display to read the labels and then could not translate back which feed was which when asked to predict performance of heaters 1 and 2.

1. [I] expected 1-5 from front to back, not the other way.

1. The use of 3-D here made the graph very difficult to interpret. [It was] labor intensive to manipulate [the graph] to see bends [in the data feeds].

1. Heater labels and strips should have matching color coding (as on the 2D strip chart).

1. In operations, red is used to denote out-of-limit values. [Green is used for within-limits values and yellow for values trending toward red.]

1. Labels are hard to read.

1. [I] got the same information from the 2D strip chart.