Half Damage with Recalled Rolls?

Hello smart people of Roll20 has anyone got any ideas on how to do a half damage kind of thing for spells, this is what I got at the moment and it does not work at all.. &{template:default}{{name=Arc}} {{Attack Roll = ?{Roll Type|Normal, [[1d20]]|Advantage,[[2d20kh1]]|Disadvantage, [[2d20kl1]]}+[[@{spell_attack_bonus}]]}} {{Main Target Damage = [[[[round((@{level} + 1) / 6 + 0.5)]]d8]]Lightning}} {{Second Target Damage = ($[[3]]/2)Lightning}}

You can't use any $[[#]] in formulas -- they becomes simple text objects.  So you'll have to create a roll that has all  of the rolls you want and then reference them later. 

This is why macros using the Reusing Rolls technique often have separate rolls not included in any {{ }} brackets. So you do, for instance: &{template:default}{{name=Arc}} {{Attack Roll = [[ ?{Roll Type| Normal, 1d20 | Advantage,2d20kh1| Disadvantage,2d20kl1}+@{spell_attack_bonus}]]}} [[round( [[ [[round((@{level} + 1) / 6 + 0.5)]]d8]]/2)]] {{Main Target Damage = $[[2]] Lightning}} {{Second Target Damage = $[[3]] Lightning}} I'm a little puzzled by that +0.5 on the round function. You can use ceil (round up) or floor (round down) to round in specific ways. In your current formula you'd start with 1d8, 2d8 at level 5, 3d8 at level 11, 4d8 at level 17. Is that correct? If so, a simpler expression would be ceil((@{level} + 2) / 6 )