[Help] Character sheet not subtracting a negative number.

I have the following code: <td><input type="number" name="attr_snaps_target_total" value="@{wpn_accr_tar} - @{snaps_mod} - @{shoottier}" disabled="true"></td> <td><input type="number" name="attr_snaps_mod" title="@{repeating_weapon_X_snaps_mod}" style="width: 80px;" value='-1'></td> Basically the second value (@snaps_mod) is negative and is subtracted from the value of the first one. This is part of a repeating set of weapons. If I modify the value from -1 to 0 it works. If I edit the number on the character sheet down to -1, then the output for the first value goes blank.

The sheets do not like subtracting a negative.  Its that whole double negative, divide by zero sort of thing.  Instead, add the negative.  (4) + (-2) = 2.  If the input number is negative, it will be subtracted from the total. <td><input type="number" name="attr_snaps_target_total" value="@{wpn_accr_tar} + @{snaps_mod} + @{shoottier}" disabled="true"></td> <td><input type="number" name="attr_snaps_mod" title="@{repeating_weapon_X_snaps_mod}" style="width: 80px;" value='-1'></td>