No, the reason we use positive and negative degrees is that our system calculates for both uphill and downhill firing. While they are similar, the solutions are not exact for each scenario. The system also takes in to account the slowing of the bullet, and the changes in pressure as you go higher/lower in altitude. Giving you a more precise solution vs the improved rifleman’s rule. For more on this read Chapter 4 of Applied Ballistics for Long Range Shooting 3rd Edition.