Pursuit Race Start Times

Originally posted by Phat Bouy Originally posted by john.d.knight the computer will sound the start guns rounded to the nearest second!. Just a note of caution - PC clocks are notoriously inaccurate, the timing interval is not always exactly the same.

But surely this will be more acurate than rounding to the nearest minute?

At my club we have 2 systems. The first is a computer system as per Aldridge that is used in the same way for handicap races, and can be used for pursuits. The second is a control unit ( PLC ) from a conveyor system that is used just for pusuit races. The PLC does seem to be the more accurate.

Back to the original question...... Rounding times means that as a percentage of the total time sailed the faster boats may be heavier penalised given the amount of the rounding, but in the greater scheme of things does it really matter.

I am not convinced that pursuit racing is all that fair on the fast boats anyway.

To clarify a little more, what constitues a second on a PC clock is rarely the same each time. Machines now run a rate of several Giggle Hurts (big numbers) ie calculations per second (small number). If the processor runs at a frequency that is a harmonic of mains power then other discrepancies can kick in. Not withstanding that, the inbuilt maths co-processor also has errors (just gotta lurve computers...)  get the sq root of 2 (1.4142 ....) then square it, answer = 1.99999...Gotta stop now, terrible whiff of sandals

Firstly on averge over the 2 - 3 hours a PC clock will be running it will not be that inaccurate.  At any specific time there may be greater inaccuracies because of interrupts/disk activities etc but this is still probably less than human inaccuracies with a stop watch provided the PC is just carrying out the timing task.  There are also some fairly simple ways to improve timing accuracy if you wish.

Secondly if my memory is correct the square root of 2 is irrational and therefore you will get rounding errors in this type of calculation when done on a PC.  Although many applications can handle something this simple (ie Excel, MS's Calculator) If you want to carryout accurate maths on a PC with lots of significant digits you need to be more sophisticated and use specially written modules to overcome the limits of the internal PC architecture.

Really you're nit picking who cares about 0.2 seconds compared to errors of 20 or 30 seconds and who's worried about an error of 0.00000000001% in the calculations (this is smaller than rounding errors on pocket calculators caused by having only 8 or 12 digits in the display.

Any half decent real-time programmer could write you something that was indistinguishable from the human with stop watch and fog horn.  PCs have been doing data aquisition at KHz for years 1/1000 second and I expect they are now capable of MHz 1/1,000,000 second.

Garry - Ex control and instrumentation engineer.