I can't decide if that's an excellent analogy or a terrible one. On the one hand it's very true, on the other hand I suspect the fraction of HN readers who are familiar with tank armor is fairly small.

For those not familiar, RHA is the type of armor used circa world-war II. Armor has gotten better on a per-inch-thickness with improved technology. Modern tanks (and modern anti-tank munitions) are often rated as to the equivalent thickness of RHA protection (or penetration) they provide.

For example, Explosive Reactive Armor (ERA) can have a very high RHA rating if you use a traditional HEAT (High-Explosive Anti-Tank) round as your benchmark, but a tandem HEAT round can almost completely eliminate the per-thickness protection advantage that ERA offers. So a tandem HEAT round might have a lower RHA penetration rating than a traditional HEAT round, yet be more effective against an ERA with a very high RHA rating.

So, if you have a spiffy new tandem HEAT round, and want to fake^H^H^H^H present good numbers, you find the highest RHA rated ERA armor that it can penetrate and claim that as the RHA rating of your projectile. Even though it might not be able to penetrate that many inches of actual RHA, or possibly even modern composite armor with such an RHA rating.