2 added 39 characters in body

# Ohm, 2020 19 bytes (CP437), non-competing

EDIT: Saved 1 byte by changing a map block to repeated single-component maps.

Would probably be quite a bit shorter if I had implicit vectorization.

▓_x»x»};{»úΓXΓHδ▓_~21*


Explanation:

▓_x»x»};{»úΓXΓHδ▓_~21*    Main wire, arguments: s

▓ »x  ;                  MapConvert char codes of s over...
_x                      Convert to hex
»}                     Split intodigit digitspairs
{                 Flatten
»ú               Convert digits back to base 10
ΓXΓH           Append and prepend with -1
δ          Get deltas between each element of array
▓         Map array over...
_~21*      Negate, multiply by 21


# Ohm, 20 bytes (CP437), non-competing

▓_x};{»úΓXΓHδ▓_~21*


Explanation:

▓_x};{»úΓXΓHδ▓_~21*    Main wire, arguments: s

▓   ;                  Map char codes of s over...
_x                      Convert to hex
}                     Split into digits
{                 Flatten
»ú               Convert digits back to base 10
ΓXΓH           Append and prepend with -1
δ          Get deltas between each element of array
▓         Map array over...
_~21*      Negate, multiply by 21


# Ohm, 20 19 bytes (CP437), non-competing

EDIT: Saved 1 byte by changing a map block to repeated single-component maps.

Would probably be quite a bit shorter if I had implicit vectorization.

»x»}{»úΓXΓHδ▓_~21*


Explanation:

»x»}{»úΓXΓHδ▓_~21*    Main wire, arguments: s

»x                    Convert char codes of s to hex
»}                  Split digit pairs
{                 Flatten
»ú               Convert digits back to base 10
ΓXΓH           Append and prepend with -1
δ          Get deltas between each element of array
▓         Map array over...
_~21*      Negate, multiply by 21

1

# Ohm, 20 bytes (CP437), non-competing

▓_x};{»úΓXΓHδ▓_~21*


Explanation:

▓_x};{»úΓXΓHδ▓_~21*    Main wire, arguments: s

▓   ;                  Map char codes of s over...
_x                      Convert to hex
}                     Split into digits
{                 Flatten
»ú               Convert digits back to base 10
ΓXΓH           Append and prepend with -1
δ          Get deltas between each element of array
▓         Map array over...
_~21*      Negate, multiply by 21
`