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Features Comparison for Four Mechanical Scales, and Recommendations
by David W. Davenport, 14-FEB-2000
           
    Three "Pocket" Scales Lab-Quality Bench Scale
Item # Item Description Accura Calibrön Deering Ohaus 310-00
           
1 Model/Designation Twin Beam Gram/Carat Scale Precision Twin Beam Gram Scale 10 Gram Scale Dial-O-Gram 310 Model, # 310-00
2 Price (at www.balances.com, December, 2000. Quantity discounts available) $14.00 $19.95 $25.00 $243.75 (Note that a "sister model" is the Cent-O-Gram 311 Model, # 311-00, with 4-beams—NO dial & vernier— $201.00)
3 Weighing Capacity 4 grams (20 carats) 4 grams (20 carats) 10 grams (50 carats) 10 grams (tested). Maximum is 310 grams—10 to 310 g NOT tested
4 Readability (smallest marked unit) 0.025 g intervals: black lines on a silver background 0.025 g intervals; black lines on an off-white background 0.01 g intervals; black lines on a white background 0.01 g intervals; match two sets of white lines on a black dial & vernier
5 Practical readability limit (for most users) 0.0125 g 0.0125 g 0.01 g 0.01 g
6 Accuracy for </- 1 gram ± 0.025 g ± 0.0125 g ± 0.01 g ± 0.017 g
7 Accuracy for > 1 gram ± 2.8% ± 1.25% ± 1.5% ± 0.7%
8 Accuracy, Full Range, by Linearity and Correlation Coefficient (R2) Extremely good linearity—1.9% slope error, 0.2% y-intercept error. Excellent Correlation Coefficient Excellent linearity—0.8% slope error, 0.2% y-intercept error. Excellent Correlation Coefficient Excellent linearity—0.4% slope error, 0.1% y-intercept error. Excellent Correlation Coefficient Excellent linearity—0.0% slope error, 0.1% y-intercept error. Excellent Correlation Coefficient
9 Indicator pointer Line-up end of beams with lip of base sidewall Lineup end of beams with lip of base sidewall Lineup end of beam with lip of base sidewall Lineup white indicator line with white reference line
10 Instructions for use Clear, concise. Printed on side of package Clear, concise. Printed on back of package Clear, concise. Printed on back of package Clear, concise. Eight page booklet. Includes assembly instructions
11 Dimensions (L × W × H), weight—English 4.5 × 1.875 × 0.875", 1.58 oz 4.5 × 1.75 × 0.875", 1.50 oz 5.25 × 2.94 × 1.00", 2.65 oz 15.125 × 5.50 × 12.25", 3.94 lb
12 Dimensions (L × W × H), weight—Metric 11.5 × 4.8 × 2.1 cm, 44.9 g 11.5 × 4.6 × 2.2 cm, 42.4 g 13.3 × 7.4 × 2.4 cm, 75.1 g 38.3 × 14.0 × 31.2 cm, 1,786.8 g
13 Number of Beams 2 2 1 (combination of 2) 2 "back" beams, plus dial & vernier replacing 2 "front" beams (compared to the Cent-O-Gram 311 Model)
14 Zeroing Poise Plastic, riding on back beam Plastic, riding on back beam Plastic, riding in center of beam Balance compensating knob on left side of scale
15 Weighing Poises Plastic slider on front beam. Aluminum poise-peg fits holes on back beam (or stored in "keeper" hole) Plastic slider on front beam. Aluminum poise-peg fits holes on back beam (or stored in "keeper" hole) Plastic slider on front beam, with raised bar for easier manipulation. Brass and plastic slider on back beam keys into grooves for 1 gram intervals Dial & vernier replace two "front beams" (the dial uses a spring to do the job of two beams—spring tension replaces gravity as the acting force). Windowed metal poise on each of two back beams
16 Poise Manipulation Slide front poise; position back poise in one of three holes (1, 2, or 3 g) Slide front poise; position back poise in one of three holes (1, 2, or 3 g) Slide front poise; slide back poise Use convenient dial & vernier to take all weights up to 10 g. Slide poises on two back beams for larger masses.
17 Bearing(s) and Razor(s) [Suspension system for the point of support between the beams and the sample pan] 35 mm long "plastic V-groove" bearing rests on two 7 mm long plastic "contact edges" (parts of a 33 mm long plastic razor) 35 mm long "plastic V-groove" bearing rests on two 7 mm long plastic "contact edges" (parts of a 33 mm long plastic razor) Two concave brass bearings rest on two steel-rod razors (each rod sharpened to a very fine point). Precise alignment. Agate bearings on hardened steel knives. Floating bearing design
18 Sample pan Removable, circular plastic bowl, 33 mm diameter, with a conical bottom (self-centers liquids). 19 mm tall. 8.5 ml or 1½ teaspoon capacity. Bowl has a "ring" on its bottom, outside surface, allowing it to stand by itself when removed from the balance. Two "ears" on opposite sides key into notches on the pan holder Removable, circular plastic bowl, 33 mm diameter, with a conical bottom (self-centers liquids). 19 mm tall. 8.5 ml or 1½ teaspoon capacity. Bowl has a "ring" on its bottom, outside surface, allowing it to stand by itself when removed from the balance. Two "ears" on opposite sides key into notches on the pan holder Removable, rectangular plastic bowl, 58 × 32 × 17 mm (L × W × H), with a rounded bottom (self-centers liquids). 20 ml or 4 teaspoon capacity. Bowl has flat bottom, allowing it stand by itself when removed from the balance. Two "ears" on opposite sides key into notches on the pan holder Removable, circular stainless steel pan, 99 mm diameter, with a flat bottom. 11 mm tall. 103 ml or 20½ teaspoon capacity. Has a pour spout. Flat bowl stands by itself when removed from the balance. Pan rests on plastic platform, which hangs 4" below the level of the beams. Pan support and Pan number 6993
19 Dampening mechanism (allows indicator to come to rest quickly) None None Has a "bumper" positioned below the beam, to keep the beam from swinging fully down. Magnetic force dampens movement of the indicator pointer, which settles in just 2 to 4 swings
20 Base Flat, 11.5 × 4.8 cm hard plastic surface Flat, 11.5 × 4.6 cm hard plastic surface 3-point base, hard plastic feet 3-point base, zinc feet
21 Construction materials Plastic, with 1.2874 g aluminum poise-peg Plastic, with 1.2731 g aluminum poise-peg Plastic, with attached brass poise for back beam. Brass bearings, steel razors Zinc base, aluminum beams, agate bearings, hardened steel knives, stainless steel pan, plastic and steel pan support, spiral torsion spring inside the dial
22 Scale base and cover make a sturdy case for carrying in a pocket, purse, pack, etc. Cardboard box included. Yes. Place side with tab on a table, lift-off the cover Yes. Place side with tab on a table, liftoff the cover Yes. Place side with 3 feet on a table, liftoff the cover Not Applicable—benchtop use. Not intended as a "portable" scale
23 Color Black Black Black Beige, black, red, polished steel
24 Assembly time None None None 12 minutes, 10 seconds. One required tool is included
25 Strong Points (All four scales have excellent linearity) Excellent accuracy. Tests show BETTER accuracy than the "1/20 g" = 0.05 g advertised accuracy. Least expensive model. Ties with Calibrön for "smallest, most pocketable." Fits in shirt pocket Excellent accuracy. Tests show BETTER accuracy than the "1/20 g" = 0.05 g advertised accuracy. Ties with Accura for "smallest, most pocketable." Fits in shirt pocket Excellent accuracy. Scale includes a plastic "manipulator" for moving the front poise, and assisting in dampening the swinging beam. With sliding poise on back beam, easier to perform weighings than 4 gram scales with "poise-peg and hole." The Deering has 2½ times the capacity of the 4 gram models. Fits coat pocket Excellent accuracy—BETTER than the manufacturer's specification of "± 0.035 g". Dial & vernier are far superior to all pocket models for speed and ease of weighing samples—probably 5 to 10 times faster—partly due to magnetic dampening. Scale goes up to 310 grams, for those preferring expanded capacity. Gemstone bearings. Solid construction. Ohaus offers excellent customer service, and warranty repair. Information, technical and customer support at www.ohaus.com
26 Areas for Improvement Could use a "bumper" to dampen beam movement (see Deering, Item # 19). Could use a 3-point, non-skid base. A 3 mm deep "cutout" at the corner of the base sidewall (corner closest to the "5 carats" print) would allow better viewing of the beams "lining-up" with the lip of the base sidewall . . . an aid to more accurate readings. A triangular file can make such a "cutout" Could use a "bumper" to dampen beam movement (see Deering, Item # 19). Could use a 3-point, nonskid base. A 3 mm deep "cutout" at the corner of the base sidewall (corner closest to the "5 carats" print) would allow better viewing of the beams "lining-up" with the lip of the base sidewall . . . an aid to more accurate readings. A triangular file can make such a "cutout" Could use a nonskid surface for its existing 3-point base Could use a nonskid surface for its existing 3-point base. User will require some "practice" to discern the correct reading on the vernier, which shows the "hundredths gram" value. Most primary (and many secondary) school students would find the vernier hard to understand. (The 4-beam Cent-O-Gram 311 Model is probably a better choice for those who prefer "plain" readability—just read 4 poise values from 4 beams . . . certainly the best choice for instructional demonstrations with most primary and secondary students)
27 Usage Recommendations 1. All mechanical scales should be set-up in an area free of air currents, if possible. Moving air will keep the beams swinging, so that they never truly "settle" on the reference mark.) 2. Check the "zero" on a mechanical scale frequently—between every measurement, if possible. The scale may slide slightly, somewhat changing its "level," and slightly changing its "zero." Don't lose the aluminum poise peg! Use a toothpick, small cable tie, etc. to manipulate the front poise, for ease and accuracy . . . also use the tool to dampen the swinging beams. Place base on nonskid surface, if possible. Two beams are at slightly different levels. Choose ONE beam for aligning with lip of base sidewall, when "zeroing" and taking measurements Don't lose the aluminum poise peg! Use a toothpick, small cable tie, etc. to manipulate the front poise, for ease and accuracy . . . also use the tool to dampen the swinging beams. Place base on nonskid surface, if possible. Two beams are at slightly different levels. Choose ONE beam for aligning with lip of base sidewall, when "zeroing" and taking measurements Place base on nonskid surface, if possible. CAUTION: Keep small children away from this scale! They can easily take it apart, exposing two 10 mm long steel rods with extremely sharp points . . . puncture wound hazard! Place base on nonskid surface, if possible. This scale is a real pleasure to use! With a little practice, the user can "dial-in" the correct weight with one turn of the dial, and NO "backdialing." Very fast. Store under a dust cover to preserve accuracy and increase longevity. Specific gravity determinations can be performed by this scale (and its "sister," the Cent-O-Gram 311 Model)
28 Other Notes Made in Taiwan, distributed from Illinois. Copyright 1999. This scale is based on the Calibrön scale in most every detail Made and distributed from Arizona. Copyright 1985 Made in Arizona, distributed from Illinois. Patented, no date. Holographic "Deering" stickers on box and case interior Made and distributed from New Jersey. Copyright 1982, 1998. Commonly used in schools, industry, and laboratories
29 Buying Recommendations A great buy for those desiring accuracy and a 4 gram (20 carat) capacity For a little more money, a little more accurate scale for those desiring 4 gram (20 carat) capacity For a larger investment, more weighing capacity and easier use than the 4 gram scales A "Cadillac" among mechanical scales with 0.01 g readability. An excellent choice for users not requiring portability, doing much weighing, and preferring "dial-in" speed. Main distinction between the "sister models" is that the dial & vernier (Dial-O-Gram 310 Model) have replaced two beams with poises (Cent-O-Gram 311 Model)— "dial-in" spring tension replacing gravitational force on two front beams

Summary of Accuracy Determinations for Four Mechanical Balances

Methodology and Standard Weights for Accuracy Testing on Four Mechanical Balances

The advent of lower cost high precision weigh sensors and China's ability to produce quality digital weighing scales has resulted in the manufacturer's of Calibron, Deering and other mechanical scales to cease production. We have no remaining stock on these mechanical scales and recommend for an alternative the My Weigh Palmscale 8.0 (300g x 0.01g), MyWeigh Palmscale 7.0 (200g x 0.01g) or My Weigh Durascale D2-300 (300g x 0.01g)

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