due to the low power (and the low amount of energy thus consumed). Conversely, high efficiencies (presumably at high power) get high weighting and thus count for more. This may result in a higher average efficiency than would be obtained by simply averaging efficiency over time. Another consideration is that the efficiency curves (that plot efficiency vs. current) tend to drop off rapidly at both low current and very high current for traction motor efficiency, and at low power for gear efficiency) so it is not a linear relationship. Investigations for diesel locomotives show that the lower notches (except notch 0 which is "motor off") of the controller (and especially notch 1 – the lowest power) are much less used than the higher notches. At very high currents, the resistive loss is high since it is proportional to the square of the current. While a locomotive may exceed the nominal current, if it goes too high the wheels will start slipping. So the unanswered question is just how often is nominal current exceeded and for how long? The instructions for starting a train from a stop suggest exceeding the current where the wheels would normally start to slip, but to avoid such slipping by putting sand on the rails (either automatically or by depressing a "sand" button just as the wheels start to slip). Inspecting a graph of traction motor gear efficiency shows 98% efficiency at nominal power but only 94% efficiency at 30% of nominal power. To get the efficiency of the motor and gears (connected in series), the two efficiencies must be multiplied. If the weighted traction motor efficiency is 90%, then 90% x 94% = 85% (very rough estimate) which is not too much lower than that estimated the 90% supporters mentioned above. If per the table 75% of power to the substation reaches the locomotive motors then 75% x 85 = 64% (roughly) of the power to the substation (from the USSR's power grid) reaches the wheels of the locomotives in the form of mechanical energy to pull the trains. This neglects the power used for "housekeeping" (heating, lighting, etc.) on passenger trains. This is over the whole range of operating conditions in the early 1970s. There are a number of ways to significantly improve this 64% figure and it fails to take into account savings due to regeneration (using the traction motors as generators to