I like using a scale.
The one on the link is very expensive. Here's the one that I use $9.25

http://www.amazon.com/American-Weigh-Signature-Series-Digital/dp/B002SC3LLS/ref=sr_1_3?ie=UTF8&qid=1342197188&sr=8-3&keywords=digital+scale

I've had two. The first one I left out in the rain a couple of times. I've found that this cheap digital scale is very accurate (I've compared it to a $200 digital scale), stays on longer than the more expensive scales.

The method I use is.
I place a plastic cup (1-8 ounce batch) or yogurt container (up to a quart) on the scale. I turn it on. This zeros out the scale cancelling out the weight of the cup.

I pour in as much epoxy resin as I want for the batch. I read the scale.
Then I refer to my weight chart and add the hardener.
If the scale says 2.31 ounces, grams, jins, whatever .... (units do not matter so long as you're consistent)
I look for 2.3 on my chart. For WestSystems 205 Fast hardner it says I need .46 (same units) of hardener, total 2.76, so I pour in hardener until I hit 2.76. Usually I'll over do it and it will go to 2.8 or 2.9 I don't know what the margin of error is, but I've haven't had any problems

If the scale turns off (it'll do this in something like 2 minutes, so long as I remember the first number (Resin) I can then turn on the scale, which will go to zero and then just add the Hardener.
I usually loosely wrap my scale with a piece of saran wrap to keep it clean.

The pump and condiment squeeze bottles are a good idea. I usually over pour from my resin and hardener cans.

I'll cut and paste my WEST Systems 105 Resin, 205 Fast Hardener spreadsheet. (And at the bottom I'll paste my 105 Resin, 207 Special Hardener
The fast ratios are easy 5:1 volume and weight, the Slow 207 (I can't even remember the volume ratio) the weight ratio is 3.7:1
I print up my spreadsheets put them back to back in a gallon zip lock.

Fast Hardener 205 Resin 105
5:1 Volume & Weight
105 205 Oz, g, any unit
Resin Hardener Total
0.50 0.10 0.60
0.60 0.12 0.72
0.70 0.14 0.84
0.80 0.16 0.96
0.90 0.18 1.08
1.00 0.20 1.20
1.10 0.22 1.32
1.20 0.24 1.44
1.30 0.26 1.56
1.40 0.28 1.68
1.50 0.30 1.80
1.60 0.32 1.92
1.70 0.34 2.04
1.80 0.36 2.16
1.90 0.38 2.28
2.00 0.40 2.40
2.10 0.42 2.52
2.20 0.44 2.64
2.30 0.46 2.76
2.40 0.48 2.88
2.50 0.50 3.00
2.60 0.52 3.12
2.70 0.54 3.24
2.80 0.56 3.36
2.90 0.58 3.48
3.00 0.60 3.60
3.10 0.62 3.72
3.20 0.64 3.84
3.30 0.66 3.96
3.40 0.68 4.08
3.50 0.70 4.20
3.60 0.72 4.32
3.70 0.74 4.44
3.80 0.76 4.56
3.90 0.78 4.68
4.00 0.80 4.80
4.10 0.82 4.92
4.20 0.84 5.04
4.30 0.86 5.16
4.40 0.88 5.28
4.50 0.90 5.40
4.60 0.92 5.52
4.70 0.94 5.64
4.80 0.96 5.76
4.90 0.98 5.88
5.00 1.00 6.00
Resin Hardener Total
5.00 1.00 6.00
5.25 1.05 6.30
5.50 1.10 6.60
5.75 1.15 6.90
6.00 1.20 7.20
6.25 1.25 7.50
6.50 1.30 7.80
6.75 1.35 8.10
7.00 1.40 8.40
7.25 1.45 8.70
7.50 1.50 9.00
7.75 1.55 9.30
8.00 1.60 9.60
8.25 1.65 9.90
8.50 1.70 10.20
8.75 1.75 10.50
9.00 1.80 10.80
9.25 1.85 11.10
9.50 1.90 11.40
9.75 1.95 11.70
10.00 2.00 12.00
10.25 2.05 12.30
10.50 2.10 12.60
10.75 2.15 12.90
11.00 2.20 13.20
11.25 2.25 13.50
11.50 2.30 13.80
11.75 2.35 14.10
12.00 2.40 14.40
12.25 2.45 14.70
12.50 2.50 15.00
12.75 2.55 15.30
13.00 2.60 15.60
13.25 2.65 15.90
13.50 2.70 16.20
13.75 2.75 16.50
14.00 2.80 16.80
14.25 2.85 17.10
14.50 2.90 17.40
14.75 2.95 17.70
15.00 3.00 18.00
15.25 3.05 18.30
15.50 3.10 18.60
15.75 3.15 18.90
16.00 3.20 19.20

207 SLOW Special Hardener
Slow Hardener 207
3.7 : 1 by weight WEST Epoxy
105 207
Resin Hardener Total
0.25 0.07 0.32
0.30 0.08 0.38
0.35 0.09 0.44
0.40 0.11 0.51
0.45 0.12 0.57
0.50 0.14 0.64
0.55 0.15 0.70
0.60 0.16 0.76
0.65 0.18 0.83
0.70 0.19 0.89
0.75 0.20 0.95
0.80 0.22 1.02
0.85 0.23 1.08
0.90 0.24 1.14
0.95 0.26 1.21
1.00 0.27 1.27
1.05 0.28 1.33
1.10 0.30 1.40
1.15 0.31 1.46
1.20 0.32 1.52
1.25 0.34 1.59
1.30 0.35 1.65
1.35 0.36 1.71
1.40 0.38 1.78
1.45 0.39 1.84
1.50 0.41 1.91
1.55 0.42 1.97
1.60 0.43 2.03
1.65 0.45 2.10
1.70 0.46 2.16
1.75 0.47 2.22
1.80 0.49 2.29
1.85 0.50 2.35
1.90 0.51 2.41
1.95 0.53 2.48
2.00 0.54 2.54
2.05 0.55 2.60
2.10 0.57 2.67
2.15 0.58 2.73
2.20 0.59 2.79
2.25 0.61 2.86
2.30 0.62 2.92
2.35 0.64 2.99
2.40 0.65 3.05
2.45 0.66 3.11
2.50 0.68 3.18
2.55 0.69 3.24
Resin Hardener Total
2.50 0.68 3.18
2.60 0.70 3.30
2.70 0.73 3.43
2.80 0.76 3.56
2.90 0.78 3.68
3.00 0.81 3.81
3.10 0.84 3.94
3.20 0.86 4.06
3.30 0.89 4.19
3.40 0.92 4.32
3.50 0.95 4.45
3.60 0.97 4.57
3.70 1.00 4.70
3.80 1.03 4.83
3.90 1.05 4.95
4.00 1.08 5.08
4.10 1.11 5.21
4.20 1.14 5.34
4.30 1.16 5.46
4.40 1.19 5.59
4.50 1.22 5.72
4.60 1.24 5.84
4.70 1.27 5.97
4.80 1.30 6.10
4.90 1.32 6.22
5.00 1.35 6.35
5.10 1.38 6.48
5.20 1.41 6.61
5.30 1.43 6.73
5.40 1.46 6.86
5.50 1.49 6.99
5.60 1.51 7.11
5.70 1.54 7.24
5.80 1.57 7.37
5.90 1.59 7.49
6.00 1.62 7.62
6.10 1.65 7.75
6.20 1.68 7.88
6.30 1.70 8.00
6.40 1.73 8.13
6.50 1.76 8.26
6.60 1.78 8.38
6.70 1.81 8.51
6.80 1.84 8.64
6.90 1.86 8.76
7.00 1.89 8.89
7.10 1.92 9.02