This is a spinoff from the "how can we trust any of them" computer thread.
Uncle Pug made the observation that use of ascent rate indicators introduces hysteresis. A discussion sort of started but got stalled, but I'm still curious about this. I would have PM'd UP, but he seemed to want to continue the discussion publicly, so excuse me if this is too obsessive to interest anybody else
I assume the reference is to one of two things: Either the ascent rate indicator is lagging the actual ascent rate, or the diver's response lags from the indicator.
Thinking this through: My computer samples every twenty seconds. It requires at least two values to calculate a rate of change. The calculation is going to be, from my viewpoint, done instantaneously, and I would assume the refresh rate on the screen is also effectively instantaneous. But twenty seconds is a fair amount of time, and if my ascent rate is accelerating during that time, for example, the indicator will show me the average rate for the period. In the time it takes me to look at the indicator and decide on my reaction, my ascent rate may be quite a bit higher than what I saw and I may not intervene enough to slow it. Or, if I've slowed, I may intervene too much, in either case creating a mismatch between rate and response.
In addition, of course, the diver's intervention is not instantaneously effective because of momentum and water resistance.
I'm assuming these factors are what UP was referring to as being the problem with using ascent rate indicators alone. So the question remains, what is the best feedback to allow the diver to most closely control ascent rate? Seems to me that a visual reference is ideal, assuming the diver has any sense of scale on it. But a visual reference is not always available. Can you learn to interpret sensations carefully enough to calibrate them? I mean, I know if I am descending rapidly because of the rate of increase of pressure in my ears -- but that doesn't work for ascents because my ears clear themselves continuously and I don't feel it. Loosening of the dry suit will tell me I've ascended but not how fast . . . UP, what say you?
Uncle Pug made the observation that use of ascent rate indicators introduces hysteresis. A discussion sort of started but got stalled, but I'm still curious about this. I would have PM'd UP, but he seemed to want to continue the discussion publicly, so excuse me if this is too obsessive to interest anybody else
I assume the reference is to one of two things: Either the ascent rate indicator is lagging the actual ascent rate, or the diver's response lags from the indicator.
Thinking this through: My computer samples every twenty seconds. It requires at least two values to calculate a rate of change. The calculation is going to be, from my viewpoint, done instantaneously, and I would assume the refresh rate on the screen is also effectively instantaneous. But twenty seconds is a fair amount of time, and if my ascent rate is accelerating during that time, for example, the indicator will show me the average rate for the period. In the time it takes me to look at the indicator and decide on my reaction, my ascent rate may be quite a bit higher than what I saw and I may not intervene enough to slow it. Or, if I've slowed, I may intervene too much, in either case creating a mismatch between rate and response.
In addition, of course, the diver's intervention is not instantaneously effective because of momentum and water resistance.
I'm assuming these factors are what UP was referring to as being the problem with using ascent rate indicators alone. So the question remains, what is the best feedback to allow the diver to most closely control ascent rate? Seems to me that a visual reference is ideal, assuming the diver has any sense of scale on it. But a visual reference is not always available. Can you learn to interpret sensations carefully enough to calibrate them? I mean, I know if I am descending rapidly because of the rate of increase of pressure in my ears -- but that doesn't work for ascents because my ears clear themselves continuously and I don't feel it. Loosening of the dry suit will tell me I've ascended but not how fast . . . UP, what say you?
