User`s guide

E-Prime User’s Guide
Appendix A: Timing Test Results
Page A-6
Having a well-configured machine is critical for achieving accurate timing during the run of an
experiment. Figure 4 illustrates the importance of the configuration of the hardware and how
dramatically it can impact millisecond precision.
Missed Clock Ticks
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50
Sequential Run
Milliseconds Lost
With network
connected
Without network
connected
Figure 4. Missed ticks test of 10,000 ticks on a computer with an ill behaved network card. Runs with and without the
network connected.
The test was run on a Pentium 120 MHz computer with an outdated and ill behaved network card
and driver pair. The loss on the first run was 5866 of 10000ms. Thereafter, the typical loss rate
was 290ms with a peak loss (at run 37) of 2927ms. On the same machine with the network card
disconnected, the missed tick rate was 43 of 10000ms on the first run, and thereafter averaged
5ms with a worst case of 9ms. Although this computer is capable of delivering millisecond
accuracy, it cannot do so with the installed network card and version of the network software.
Better network cards and drivers on other machines can provide millisecond precision while
supporting network activity. One of the reasons for doing long duration tests (e.g., 6 hours) is to
see if a system is sensitive to the behavior of other devices on the network.
Figures 5a – 5c display a variety of timing error patterns for 3 different computers during the six-
hour time test. A perfect run would be a straight line, indicating that there was no loss of ticks
during the run. Of the three computers, the fastest machine (greater than 266 MHz) resulted in a
good time profile with losses between 0% and 0.01% (Figure 5a). The second machine shows
generally a stable performance with a 25.81% missed tick rate at run 399 (Figure 5b). The timing
test run on the third machine resulted in a repeating pattern of increasing loss of ticks ranging
from 2% to 4% (Figure 5c).