Guess it's time to start with some of the articles I've been delaying...
Honest and Blackwing - Kalut the Moon Shadow have very similar effects. They both have a Quick Effect that you can activate during the Damage Step in order to increase the ATK of your battling monster. In general, they should be very simple to understand, but their interaction with mutiple copies of themselves, or interactions between the two aren't that simple. Like all common disputes, they occur due to poor communication between the players, as you will see in a minute that they aren't as hard as most people make them to be.
Both Cards can be activated since the Start of the Damage Step until Damage Calculation inclusive. The first three Sub-Steps ("Start of the Damage Step", "Flip the monster Face-up", and "Before Damage Calculation") aren't as problematic as the last one ("Damage Calculation"). Remember that During Damage Calculation, only one manual chain can be started, so you and your opponent can only build one chain with your copies of Honest or Kalut at that Sub-Step, and then, you would have both monsters battle each other. However, during the previous Sub-Steps, there is always one more chance to start a new chain, as the "Before Damage Calculation" Sub-Step allows any number of manual chains.
The above paragraph covers most of the problems that you will find between multiples copies of Honest, or multiple copies of Kalut. The problem is that it's a little abstract, so let's look at some examples:
1) Player A declares an attack with Blackwing - Shura the Blue Flame onto Player B's Blackwing - Blizzard the Far North. During Damage Calculation, Player B activates his Kalut (Kalut #1). Player A chains a Kalut of his own (Kalut #2), to which Player B chains Divine Wrath. Resolving this chain backwards, Kalut #2 has its effect's activation negated, and Kalut #1 increases the ATK of Blizzard the Far North. Now, Shura has 1800 ATK, and Blizzard has 2700 ATK. Since only one chain can be manually started at the Damage Calculation Sub-Step, Player A cannot activate another copy of Kalut. The monsters will then battle, and Player A will lose 900 Life Points and his Shura in battle.
2) Player A declares an attack with Cyber Dragon onto Player B's Gladiator Beast Heraklinos. During Damage Calculation, Player A activates his Honest. Player B activates Gladiator Beast War Chariot. Resolving this chain, Honest has its activation negated. Since only one chain can be manually started at the Damage Calculation Sub-Step, player A cannot activate another copy of Honest. The monsters will then battle, and Player A wil lose 900 Life Points and his Cyber Dragon in battle.
Wow, 900 again? What a coincidence Q_Q
3) Player A declares an attack with Cyber Dragon onto Player B's Gladiator Beast Heraklinos. During the "Before Damage Calculation" Sub-Step, Player A activates his Honest (Honest #1). Player B activates Gladiator Beast War Chariot. Resolving this chain, Honest #1 has its activation negated. Since this Sub-Step allows any number of manual chains, Player A can now activate a second copy of Honest. After Honest resolves, Cyber Dragon will have 5100 ATK.
4) Player A declares an attack with Blackwing - Bora the Spear onto Player B's Blue-Eyes White Dragon. During the "Before Damage Calculation", Player A activates his Kalut (Kalut #1). Player B activates Divine Wrath. Resolving this chain, Kalut #1 has its activation negated. Since this Sub-Step allows any number of manual chains, Player A can now activate a second copy of Kalut (Kalut #2). Player B then chain Forbidden chalice, targeting his own Blue-Eyes White Dragon. Resolving this chain, Blue-Eyes has 3400 ATK, while Bora has 3100 ATK.
As you can see, most scenarios come down to whether you are in the "Before Damage Calculation" Sub-Step, or the "Damage Calculation" Sub-Step. Activating these Cards during the "Damage Calculation" Sub-Step gives you more safety, as very little Cards can be activated at that time (for example, Forbidden Chalice cannot be activated). However, if your Kalut or Honest is negated, then you will have to battle with your monster's usual ATK, which probably sucks for this situation. On the other hand, activating your effect at the "Before Damage Calculation" Sub-Step gives you room for a second Kalut or Honest, but at the same time, it opens the floodgates for a number of other ATK/DEF modifiers to be chained. Specially, a wise opponent that will wait until the "Damage Calculation" Sub-Step, as we will see in a minute.
The interaction between multiple copies of each Card can also be troublesome. Multiple Kaluts aren't problematic, as Kalut always adds the same amount of ATK. It's basic algebra, and even a hardcore hater of algebra like me knows that this is simple. If you have two Blackwings battling each other, no matter the number of Kaluts that each player uses, it all comes down to adding 1400 ATK a number of times. Even if a player activated 152 Kaluts and the other chained 547 Kaluts of his own, one can still figure out the final ATK for each monster. The actually troublesome guy is Honest. Honest's ATK boost is not a fixed number, and actually chaining it among other modifiers can become a nightmare. Let's look at some examples:
1) Player A's Cyber Dragon attacks Player B's Blue-Eyes White Dragon. During "Damage Calculation", Player A activates Honest (Honest #1), and Player B chains Honest (Honest #2). Resolving backwards, Honest #2 checks for Cyber Dragon's ATK, and adds that value to BEWD's ATK (3000+2100 = 5100). Now, Honest #1 resolves, and checks BEWD'S ATK, to add that value to Cyber Dragon's ATK (2100 + 5100 = 7200). In the end, Blue-Eyes White Dragon is destroyed and Player B takes 2100 points of damage. The lesson here: Do not chain ATK bonuses to Honest. Ever.
2) Player A's Cyber Dragon attacks Player B's Blue-Eyes White Dragon. During the "Before Damage Calculation", Player A activates Honest (Honest #1). Player B does not respond. Cyber Dragon's ATK is now 5100. Then, gameplay proceeds to the "Damage Calculation" Sub-Step, and Player B wishes to activate Honest (Honest #2) now. Honest #2 resolves, providing Cyber Dragon's ATK to BEWD. Blue-Eyes ends up with 8100 ATK. Cyber Dragon is destroyed in battle, and Player A takes 3000 points of damage.
So what happened here? Honest #2 was not chained to Honest #1. Therefore, the ATK bonus for BEWD was composed of Cyber Dragon's Original ATK AND the bonus that Honest #1 provided. In the previous scenario, Player B did not have this opportunity, because the scenario happened at the "Damage Calculation" Sub-Step, and once this chain is over, the monsters will battle without another opportunity to activate more copies of Honest. These two scenarios once again show a key difference on why it is important to choose between both Sub-Steps.
Leaving the math aside, the problem comes down to how to determine the order, and the Sub-Step you are currently at. Scenarios like this show why it is crucial that both players clearly communicate their moves. You won't believe how helpful it is to explain that you are moving into the Damage Step, and through which Sub-Steps. You don't need to memorize the whole chart, just explain that you are moving into the "Before Damage Calculation" Sub-Step, and then into the "Damage Calculation" Sub-Step. Remember that most battles involve moving through the Damage Step, so you are not giving away any information by announcing that you will enter a certain Sub-Step. As if it wasn't suspicious enough to attack a monster with twice the ATK of your monster. So go ahead and spill some saliva explaining what on earth you wish to do.
The order of the effects is chosen by priority. Upon entering a Sub-Step, the turn player has priority to activate his/her effects, or to pass priority to the opponent. To avoid more mathematical annoyances, the pro-tip is that if you are attacking and you wish to use Honest or Kalut, the most convenient action to take is to use your priority to activate these Cards upon entering Damage Calculation. Kalut is more likely to fail if one considers every scenario, but that's more of a tactical thing.
Ugh...what a dense topic. If you have any questions, feel free to drop me an e-mail at ness00[at]gmail[dot]com.