The various stations that I use all have a tipping bucket style gauge.
One way of determining rate depends upon the time between tips, and when you have a real frog strangler going on, it tips mighty fast. At those very high rates of fall even a few tenths of a second variation can imply a very high rate. The method of timing is not as accurate because the fast tips means that some variation in the collection occurs, and that makes calculating an accurate rate, at high rates, more difficult. I would guess from the way this method is done that it would tend to UNDER estimate the rate, and UNDER collect, with the actual accumulation being a wee bit higher.
The other way to determine rate is to compromise on instantaneous rate (using time between tips) is to take a chosen time period, perhaps a minute or five minutes, look at the rain received during that chosen interval, and expand it to what an hour would be. While this gets rid of the variation in tipping rate, it does not have the capability of giving an instantaneous rate. If you got 0.2" in five minutes, then 20x that would be your hourly rate. But what happens if that 0.2" occured in two minutes from a very heavy downpour, and for the rest of the timing period the real rate was much slower?
But other than curiosity, rate differences that short really don't make much of a concern. If you live in erosion prone areas, a sustained rate is much more worrisome.
Indeed, here in the MidWest USA, it can fall at the RATE of 10-12 inches per hour (sort of hurricane wx), but it is for only a few minutes out of the whole storm. I think the most I've seen in the past decade has been around 11"/hour, and the storm total was a whopping (for us) 3 1/2", in less than an hour. The integral of the rate over the period is the whole accumulation, of course, and the derivative is the rate, take your pick.
We've not had an old fashion gusher here in awhile, but so far this year I've had a couple brief indication of 8"/hour rates. I usually have to rush to see the readouts of rate since by the time I hear it raining that hard, and get down to the stations, the deluge is already letting up.
A real indicator for me is to look at the debris and sand on on the road on the hill. When it has washed a path or has washed away some of the roadside along the rural crowned asphalt road, then I know it was a real rate, with that amount of water needed to be cascading down (eroding), and then I am thankful that it was only for three to five minutes at that rate.
For those in hurricane-land, what are the sustained rates at the height of the storm? I remember hearing the talking Wx heads saying rates of 10", sustained, could be seen. How long does that go on?
Good thing Florida is mainly flat.
Obviously a non-reporting (unlike tipping bucket, RM Young capacitance, weighing bucket are reporting types) gauge cannot report a rate. You'd have to take timed measurements and do the differential yourself. Plotting and getting a slope is the same thing. And the station uses whatever method of taking the time between tips, or the amount over the last minute/five minutes, etc, whatever the designer chose for a time interval, to see the rate. And it is the station making use of the reported rain to calculate the rate, not the gauge itself.
I haven't timed it, but when calibrating one of my tippers, I noticed that after the high rate I caused by dumping some through, after I stopped adding water to the funnel, the rate still clicked down towards zero, so that station was using the method of amount of rain in the last several minutes rather than the time between tips, which I would agree would be more likely to be a better method. I just didn't have the foresight to time how long it took for the rain rate to decrease to zero after the last water was run through the gauge. Hmm, another thing to try after I get the other projects caught up.
