(approximate) cup change (and tablespoon + teaspoon) for developing film with US cup for Rollei Colorchem C-41 kit

conversions.md

Chemicals

Rollei Colorchem C-41 kit Manual

This is converted for for US measurements. I will also have my develop times on here.

Colour Developer Mixing Instructions (Converted)

Page 7 of the manual converted. This assumes you have the following US-based measurement devices:

• US cup (1, 1/2, 1/3, 1/4, 1/8)
• US tablespoon (1, 1/2)
• US teaspoon (1, 1/2)

Used the script in the gist, it's basically coin change (DP). It's not perfect, but it's pretty close.

We can't make some measurements exactly, so expect for there to be a difference; but this shouldn't be a big deal because even pouring is error prone (due to human and tool inaccuracies).

I've tried to minimise the amount of cups/instruments used. Hence why I've done it via coin change.

mL	what to use	error (mL)
50mL	1/8 cup tablespoon teaspoon	-0.625mL
100mL	1/3 cup tablespoon teaspoon	-1.25mL
200mL	1/2 cup 1/3 cup 1/2 teaspoon	-0.03125mL
600mL	2 cups 1/2 cup 1/2 tablespoon	-0.09375mL
800mL	3 cups 1/8 cup 1/4 cup	-0.125mL
950mL	4 cups	-2.0mL

NOTES:

• 50mL and 100mL would be more accurate if we had 1/6 and 1/12 of cup, but I don't so :p

Name	Water (25-45 celcius; 77F - 104F)	Part A	Part B	Part C
Color developer	800mL	100mL	50mL	50mL
Bleach (fixer)	600mL	200mL	200mL
Stablizer	950mL	50mL

Develop Times

TODO

cup_change.py

# usage:
#    python3 coin_change.py

import sys
from collections import defaultdict

CONVERT_TO_INTEGER = 100000

measurements = {
    "1cup": 237,
    "1half_cup": 118.5,
    "1quarter_cup": 59.25,
    "1third_cup": 79,
    "1eighth_cup": 29.625,

    "2tablespoon": 14.8125,
    "2half_tablespoon": 7.40625,

    "3teaspoon": 4.9375,
    "3half_teaspoon": 2.46875,
    #"quarter_teaspoon": 1.234375,
}

cup_names = {
    "1cup": 'cup',
    "1half_cup": '1/2 cup',
    "1quarter_cup": '1/4 cup',
    "1third_cup": '1/3 cup',
    "1eighth_cup": '1/8 cup',

    "2tablespoon": 'tablespoon',
    "2half_tablespoon": '1/2 tablespoon',

    "3teaspoon": 'teaspoon',
    "3half_teaspoon": '1/2 teaspoon',
}

for key, value in measurements.items():
    measurements[key] *= CONVERT_TO_INTEGER
    measurements[key] = round(measurements[key])

# ensure we have the proper conversions 
# to simplify the devices used
assert(measurements["1cup"] == 2*measurements["1half_cup"])
assert(measurements["1cup"] == 4*measurements["1quarter_cup"])
assert(measurements["1cup"] == 3*measurements["1third_cup"])
assert(measurements["1cup"] == 8*measurements["1eighth_cup"])

assert(measurements["2tablespoon"] == 2*measurements["2half_tablespoon"])

assert(measurements["3teaspoon"] == 2*measurements["3half_teaspoon"])

assert(measurements["1cup"] == 16*measurements["2tablespoon"])
assert(measurements["1cup"] == 48*measurements["3teaspoon"])


def cup_change(to_make):
    to_make *= 100000

    coins = [1000000000] * (to_make+1)
    solution = [None] * (to_make+1)

    coins[0] = 0
    for x in range(1, to_make+1):
        for name, c in measurements.items():
            if x - c >= 0 and coins[x - c] + 1 < coins[x]:
                coins[x] = coins[x - c] + 1
                solution[x] = name

    val = max([i for i, v in enumerate(range(to_make + 1)) if solution[v] is not None])
    initial_val = val

    cups = []
    result = 0
    while val > 0:
        measurement_used = solution[val]
        result += measurements[solution[val]]
        val -= measurements[solution[val]]
        cups.append(measurement_used)

    errorML = (result - to_make) / CONVERT_TO_INTEGER
    return cups, errorML

if __name__ == '__main__':

    # print everything in markdown pls
    print('| mL | what to use | error (mL)')
    print('|:---|:------------|:------------')
    for mL in [50, 100, 200, 600, 800, 950]:
        coins, error  = cup_change(mL)
        coins = sorted(coins)
        coins_counts = defaultdict(int)
        for coin in coins:
            coins_counts[coin] += 1

        coins_as_str = ''
        for coin, amount in coins_counts.items():
            # only aggregate whole measurements
            name = cup_names[coin]
            if amount > 1 and (name == 'cup' or name == 'teaspoon' or name == 'tablespoon'):
                coins_as_str += (f'{amount} {name}s')
            else:
                coins_as_str += (f'{name}')

            coins_as_str += '<br>'

        print(f'| {mL}mL | {coins_as_str} | {error}mL | ')