3.1

This definition differs from the definition ascribed to 7.2.4 (absolute angles) and the explanation given in 6.4.3. Which is correct?

3.4

This definition is not clear enough. Are non-contact portions of the surface included in this definition, such as depth vs. effective depth?

What is the term used to describe the obverse side to the “contact surface”? The measures are taken from that undefined side in Figure 15.

3.5

The method for taking “linear measures” illustrated in Figure 1 is inconsistent with the illustrations in Figure 15. Should the measure be taken on the contact surface side or the (obverse) underside?

According to the illustrations in Figure 4 a measurement parallel to the SSRP may not be parallel to the contact surface profile and will result in a measure that is longer than the actual entity.

3.6

Incorrectly numbered.

Figure 2; Ditto as 3.5! Should the measure be taken on the contact surface side or the obverse side?

According to the illustrations in Figure 4 a measurement parallel to the SSRP may not be parallel to the contact surface profile.

3.12

This is an incomplete definition because it does not account for the compensation required for any asymmetrical component.

This rule will require that more than two measurements be taken (in one direction) before the actual SSGC can be located on any contoured or molded component.

The furthest points measured along the contact surface may be located away from the center point of any contoured or molded component.

3.13

Illustrate the difference between a ”support surface reference line” and a “support surface reference plane” (3.15). Sometimes they are parallel and synonymous, other times they are perpendicular to each other.

3.16

At which location of the reference plane should a thickness measurement be taken? Consider a cushion with a built-in pelvic support or an anti-thrust wedge.

3.18

Figure 6; Ditto as 3.5! Should the measure be taken on the contact surface side or the obverse and underside?

This definition explains only the “how to” but not the “ what to” measure. The “what to” is not explained until the definitions under 7.3.3.

There are no straightforward definitions given for the subscripts “s”, “c” or “p” nor are these identified anywhere else.

A section number should be included indicating where the “symbols and abbreviated terms” are described or defined in this document.

How often will the collected data be used as a monitoring tool and what happens if (after the initial delivery) components are changed or altered by a caretaker? How do you ensure consistency if the re-measure is performed by a different person?

The global coordinate system as described in this section is positioned to represent only one quadrant of the whole for each system to be measured: WAS, SSAS and SAAS. The description offers no language for describing the other three quadrants.

The expressions YZ, ZX and XY are inconsistent. The horizontal direction should be expressed first. The XZ relationship is further reinforced in 7.3.2.

Ditto for the expressions in Figure 8.

Each illustration in Figure 8 should specify their relative axis. That is, the X-axis is represented in illustration “a” and so forth.

What is the “left hand screw rule”?

Does this system also apply to manual wheelchairs with reverse wheel configurations and front wheel drive power chairs? If so, provide an illustrated example.

The entire WAS global axis system is described in just four sentences and concludes that if it doesn’t apply it must be made to fit somehow.

Define “floor”. Does it include carpet? Must it first be plumbed for level?

Change the phrase “as desired for the user” to “as required…” or “as prescribed…”

Provide an example for “where the above description cannot be applied”.

The system (rule) for 000c seems to apply more to the axle than the “wheelchair frame geometry” as depicted in Figure 10.

Technically speaking, in illustration ‘a’, Figure 11, the location of 0,0,0s for each component is on the mid-sagittal plane, with the exception of the armrests and trunk pads.

The Note should include the origins for subscript c and p as well

There are no formal descriptions in the document which define the distance measurement for “el” or “ew”.

Though it is never stated, it appears that each component of the seating support systems required six measurements to register its spatial orientation relative to 0,0,0s. The pommel however would require from eight to ten measurements.

The definition should read “…defined by the Y and Z coordinates…”.

There is a typo in Figure 14. “ASsloc” should read “MSsloc”

In Figure 14, isn’t every component mounted below the seat in negative territory (–Z)? If not then how do you distinguish measurements between the mounting height of the lumbar support and the mounting height of the calf panel? It should be recorded as either “–Z #” or “Z –#” or “-#Z” or “# posterior Z”. Compare the armrest with the footplate measurement.

The headrest is in the negative Y position. According to the document the measurement recording would not clarify that fact.

There is also a “posterior support effective length” which should be identified here. Consider the Otto Bock OBSS system which includes a parting line between the seat and back insert, usually from 30° to 45°. This parting line renders the contact surface side for both the seat and back up to three inches shorter than the obverse side.

What is the angular relationship between a seat & back or a seat & leg support panel for a system that is configured for supine or side lying support (gurney style)?

How do you measure the absolute angle for a seat cushion with a built-in hip flexion wedge?

How do you communicate to a manufacturer that you want a seat cushion with a 10º hip flexion wedge?

Clearly there is a dominant reference direction for each support surface in reference to 0,0,0s but that is never explained to the reader.

For a supine or side lying system (gurney style), is the seat section still referred to as an inferior support and is the back section still a posterior support? If so, an additional illustration should be included to demonstrate this point. Also show the “relative angles” between components for a gurney style system.

It is not clearly explained that the axis of rotation in the sagittal plain is X.

Figure 20 is misleading. It seems to suggest that the width measurement for an inferior support is taken from the underside while a posterior support is measured from the contact surface side, and finally the superior supports are measured from the obverse of the contact surface. Which is the correct surface for recording the measures?

If the measure is taken form the contact surface of the seat insert then how do you define the width of a drop seat (DS) base that is cut to fit between the seat rails but the top layer of the foam lamination is cut full width (FW) to cover the wheelchair frame seat rails. The same is a common practice for backrest construction.

A pommel has two contact surfaces and therefore has two positions of reference in the transverse plane. But, the document never explains that.

In Figure 24 a 40º wedged pommel would be measured as simultaneously at 340° and 20°?                       (56)

Items that concern me (C) and items that bother me (B)

C

The document does not yet hint at the type of instruments used to record the proposed measures?

B

With this proposal it will require at least 50 measures to be taken just to describe the spatial orientation of components from the seat cushion and above (8 components). Now add asymmetry measurements plus all the measures for components below the seat, the wheelchair frame configuration and the postural attitude of the client. Finally, add the physical dimensions of each.

C

In engineering and CAD/CAM a circle is created counterclockwise from the horizon. Even when we measure the angle for incline or recline the zero point is on the right side of the horizon. In the ISO proposal the reference circle is created clockwise from the vertical.

B

A backrest, calf panel and t-pad positioned in space at the same orientation would produce different angular recordings. In the ISO proposal the calf panel mounted vertically would be 180° while the t-pads would be recorded at 90° and finally, the backrest angle would be 360°.

C

There is only an illustration of how “relative angles” should be recorded. There are no written instructions how the recording is taken and what to do in the case of a hip flexion wedge or other angular contour.

B

No allowance is made for even simple alterations of a planar profile in describing “relative angles”. Consider a shoulder flexion wedge.

Every element of ISO 16840-1 is written only for consideration of an upright sitting posture and only for planar (generic) systems.

I joined RESNA to be included into the world of Rehab. Not to be told that custom seating specialists have to find their own way.

A medial support has two contact surfaces for which orientation in space must be recorded separately.

A wedged shape pommel mounted slightly rotated off the Z or Y-axis will register very different measures for each side. So, which is the prevailing surface when a measure is taken in the sagittal plane?

C

None of the “linear dimensions” described in the document identify the actual location at which the measure is taken. Only that it is parallel to the “support surface reference plane”.

B

There is no clarification on where to take a measure for a component that is not symmetrical. Consider a seat with a leg length discrepancy modification.

C

ISO 16840-1 is supposed to be a document of terms and definitions and a description of symbols and abbreviations. However, it is in fact a proposal for a measuring and recording system for use in research and clinic settings.

B

I believe that if adopted by RESNA it will become a benchmark for best-practice protocol.

Critique of Annex A (normative)

The “range of typical angles” described in this annex do not account for relevant installation angles of complimentary components.

Table A.1 (sagittal views)

Why is the headrest allowed only 60º of sagittal recline angulation?

Why is the back only allowed a 300º installation angle? Why not 270º?

If the seat is allowed only a 70º installation angle then why are medial and lateral thigh supports allowed 30º.

Why is an anterior leg support allowed only 20º of extension while the posterior is allowed 90º of extension?

All posterior support components should show an absolute angle of 360º not 0º when viewed from the sagittal plane because they lye posterior to 0,0,0s and posterior to the support surface reference plane SSRP.

The item identified as a Lateral Pelvic Support is incorrectly labeled or the Absolute Angle is incorrect. (verify wording)

Figure B.1

The description for 7c is missing.

Table A.2 (frontal views)

Why is the headrest allowed only 40º of total frontal plane angulation whereas the backrest is allowed 60º?

Why is the anterior support allowed 45º of lateral angulation while the posterior support is allowed only 30º?

When viewed in the frontal plan, all right facing lateral support should show an absolute angle of 360º not 0º because they lye posterior to the support surface reference plane SSRP.

Table A.3 (transverse views)

Is 45º “typical range” sufficient for the headrest?

Clearly the anterior trunk support range is wrong.

When viewed in the transverse plan, all right facing lateral support should show an absolute angle of 360º not 0º because they lye posterior to 0,0,0s and posterior to the support surface reference plane SSRP. (10)